This book is the revised English edition of
"Szerves kemiai analizis"
published by Miiszaki Konyvkiado, Budapest
Translated by
Ildiko Egyed and Judit Gaal
JOINT EDITION P U B L I S H E D BY
ELSEVIER SCIENTIFIC P U B L I S H I N G C O M P A N Y , A M S T E R D A M , T H E
N E T H E R L A N D S A N D A K A D E M I A I K I A D 6 , THE P U B L I S H I N G H O U S E OF T H E
H U N G A R I A N A C A D E M Y O F SCIENCES, B U D A P E S T , H U N G A R Y
The distribution of this book is being handled by the following
for the U.S.A. and Canada

publishers

ELSEVIER SCIENCE P U B L I S H I N G C O M P A N Y , INC.
52, V A N D E R B I L T A V E N U E
NEW Y O R K , N E W Y O R K 10017, U.S.A.
for the East European Countries, Democratic People's Republic of Korea, People's Republic of
Mongolia, Republic of Cuba and Socialist Republic of Vietnam
Kultura Hungarian Foreign Trading Company
P.O.B. 149, H-1389 Budapest 62, Hungary
for all remaining

areas

ELSEVIER SCIENTIFIC P U B L I S H I N G C O M P A N Y
1, M O L E N W E R F
P.O. BOX 211, 1000 A E A M S T E R D A M , T H E N E T H E R L A N D S

Library of Congress Cataloging in Publication Data
Mazor, Laszlo.

Methods of organic analysis.
(Wilson and Wilson's Comprehensive analytical
chemistry; v. 15)
Rev. translation of: Szerves kemiai analizis.
Bibliography: p.
Includes index.
1. Chemistry, Analytic, 2. Chemistry, Organic.
I. Title. II. Series: Comprehensive analytical
chemistry; v. 15.
QD75.W75 vol. 15 [QD271] 543s [547.3] 81-17371
AACR2
ISBN 0-444-99704-0 (Vol. XV)
ISBN 0-444-41735-4 (Series)
© A K A D E M I A I K I A D O , B U D A P E S T 1983
All rights reserved. N o part of this publication may be reproduced, stored in a retrieval system, or
transmitted in any form or by any means, electronic, mechanical, photocopying, recording or
otherwise, without the prior written permission of the publisher.
Printed in H u n g a r y


www.pdfgrip.com

COMPREHENSIVE ANALYTICAL CHEMISTRY
ADVISORY BOARD
G. den Boef, P H . D .
Professor of Analytical

Chemistry,

University


of

Amsterdam

A. Hulanicki, P H . D .
Professor of Chemistry,

University

of

Warsaw

J. Inczedy, P H . D . , D.SC.
Professor of Analytical

Chemistry,

University

of Chemical Engineering,

Veszprem

H.M.N.H. Irving, M.A., D.PHIL., F.R.S.C.
Professor of Inorganic Chemistry,

University


of Cape

Town

G. Tolg, P H . D .
Professor of Analytical

Chemistry,

Max-Planck-Institute

for Metal Research,

D. W. Wilson, M . S C , F.R.S.C.
Formerly Head of the Department

of Chemistry,

City of London

EDITORIAL ASSISTANT
Alan Robinson, B.A.
Department

of Pharmacy,

The Queen s University

of Belfast


Polytechnic

Stuttgart


www.pdfgrip.com

Volume XV
METHODS OF
ORGANIC ANALYSIS

by
L. M A Z O R
Professor of Analytical
Chemistry
Institute for General and Analytical
Chemistry
Technical University of Budapest


www.pdfgrip.com

Wilson and Wilson's
C O M P R E H E N S I V E ANALYTICAL CHEMISTRY
Edited by

G. Svehla, P H . D., D. SC., F.R.S.C.
Reader in Analytical
The Queen s University


Chemistry
of Belfast

VOLUME XV

METHODS OF ORGANIC
ANALYSIS
BY L. MAZOR

ELSEVIER SCIENTIFIC P U B L I S H I N G C O M P A N Y
AMSTERDAM

—

OXFORD
1983

—

NEW YORK


www.pdfgrip.com

W I L S O N A N D WILSON'S

COMPREHENSIVE ANALYTICAL CHEMISTRY
V O L U M E S IN T H E SERIES

Vol. IA


Analytical Processes
G a s Analysis
Inorganic Qualitative Analysis
Organic Qualitative Analysis
Inorganic Gravimetric Analysis

Vol. IB

Inorganic Titrimetric Analysis
Organic Quantitative Analysis

Vol. IC

Analytical Chemistry of the Elements

Vol. IIA

Electrochemical Analysis
Electrodeposition
Potentiometric Titrations
Conductometric Titrations
High-frequency Titrations

Vol. IIB

Liquid C h r o m a t o g r a p h y in Columns
Gas Chromatography
Ion Exchangers
Distillation


Vol. IIC

Paper and Thin-Layer Chromatography
Radiochemical Methods
Nuclear Magnetic Resonance and Electron Spin Resonance
Methods
X-Ray Spectrometry

Vol. I I D

Coulometric Analysis

Vol. I l l

Elemental Analysis with Minute Samples
Standards and Standardization
Separations by Liquid Amalgams
Vacuum Fusion Analysis of Gases in Metals
Electroanalysis in Molten Salts


www.pdfgrip.com

Vol. IV

Instrumentation for Spectroscopy
Atomic Absorption and Fluorescence Spectroscopy
Diffuse Reflectance Spectroscopy


Vol. V

Emission Spectroscopy
Analytical Microwave Spectroscopy
Analytical Application of Electron Microscopy

Vol. VI

Analytical Infrared Spectroscopy

Vol. VII

Thermal Methods in Analytical Chemistry
Substoichiometric Analytical Methods

Vol. VIII

Enzyme Electrodes in Analytical Chemistry
Molecular Fluorescence Spectroscopy
Photometric Titrations
Analytical Applications of Interferometry

Vol. IX

Ultraviolet Photoelectron and Photoion Spectroscopy
Auger Electron Spectroscopy
Plasma Excitation in Spectrochemical Analysis

Vol. X


Organic Spot Test Analysis
The History of Analytical Chemistry

Vol. XI

The Application of Mathematical Statistics in Analytical
Chemistry
Mass Spectrometry
Ion Selective Electrodes

Vol. XII

Thermal Analysis
Part A. Simultaneous Thermoanalytical
Examinations by Means of the Derivatograph
Part B. Biochemical and Clinical Applications of
Thermometric and Thermal Analysis


www.pdfgrip.com

Vol. XIII

AAnalysis of Complex Hydrocarbon Mixtures
]Part A. Separation Methods
]Part B. G r o u p Analysis and Detailed Analysis

Vol. XIV

Ion Exchangers in Analytical Chemistry


Vol. XV

Methods of Organic Analysis

V o l XVI

-Chemical Microscopy
Thermomicroscopy of Organic C o m p o u n d s

Vol. XVII
G a s and Liquid Analysers
Vol. XVIII
Kinetic Methods in Chemical Analysis


www.pdfgrip.com

To my grandchildren Corinna
and Dominique Nobilis


www.pdfgrip.com

Preface

In Comprehensive Analytical Chemistry, the aim is to provide a work
which, in many instances, should be a self-sufficient reference work, but where
this is not possible, it should at least be a starting point for any analytical
investigation.

It is hoped to include the widest selection of analytical topics that is
possible in the compass of the work, and to give material in sufficient detail to
allow it to be used directly, not only by professional analytical chemists, but
also by those workers whose use of analytical methods is incidental to their
work rather than continual. Where it is not possible to give details of methods,
full reference to the pertinent original literature is made.
Volume XV covers one topic: organic analysis. In earlier volumes there
were some chapters devoted to this field. The Author's Preface makes it clear
that overlaps and repetitions have been avoided, as far as possible. Tlje
present text describes the subject in more depth and detail than the earlier
chapters, and covers developments which have occurred since their
publication. The author has published very successful books on the subject in
Hungarian and in English; we hope that this English version will be equally
well received. The present Editor remembers with affection those years which,
as a student and later as junior colleague, he spent in close association with
Professor Mazor.
Dr. C. L. G r a h a m of the University of Birmingham, England, assisted in
the production of the present volume; his contribution is acknowledged with
many thanks.
July, 1982

G. Svehla

xix


www.pdfgrip.com

Author's


Preface

The past fifteen years or so have seen significant developments and
transformations in the field of organic chemical analysis.
Formerly, this branch of science was favoured by manually skilled organic
chemists, usually experts in mechanics, too, who could enjoy refined manual
work combined with the satisfaction of research and development. The
diligent work of a number of outstanding researchers of this type produced
the new selective and sensitive micro-reactions in qualitative analysis and the
fast and precise quantitative micro-methods—the latter developed by the
famous Pregl school. (See: F. Pregl: Die quantitative organische Mikroanalyse, 6. Aufl., Springer, Wien, 1949).
Nowadays, not least because of skilful advertising by instrument
manufacturers, instrumental methods seem to have taken over the traditional
fields of qualitative and quantitative analysis, although experts often
emphasize that classical chemical methods still retain a definite role even
today. Undoubtedly, routine-type quantitative determinations can be
performed very well with automatic devices, in qualitative analysis the
importance of ultraviolet, infrared, N M R and mass spectrometry steadily
increases, and modern chromatographic methods also have their role to play.
Even the aforementioned chemical microanalytical methods d o not require
skilled, highly trained chemists, because all the devices, with their spare and
optional parts, are of reliable quality, even though mass produced. Their
creation formerly needed the special skill of the microanalyst. Thus, qualified
chemists may be reserved for research, development or management, while
routine work can be left to skilled technicians and assistants.
Anyone who follows the vast a m o u n t of research and development now
taking place in the field of organic analysis, but who at the same time is
familiar with the work done in industrial laboratories, would agree that
xxi



www.pdfgrip.com

because of the different requirements of industrial and research organic
chemists, the science of organic analysis is slowly splitting into two
distinguishable groups of techniques.
The first group consists of methods that still can be called chemical, being
applied mainly in industrial laboratories, where the task is to identify,
monitor the purity of, or determine the active ingredient content of raw
materials, intermediates and final products. This is partly done by
determining certain physical characteristics and partly by chemical elemental
and functional group analysis. These techniques are often augmented by U V
and IR spectrometry and by gas-liquid chromatography.
Research in organic chemistry, extending to the preparation of new
compounds, establishment of their structure and the examination of the
kinetics and mechanisms of the reactions involved, also requires the methods
mentioned in the first group, but most of the analytical work employs modern
instrumental techniques, such as mass spectrometry, high-performance liquid
and gas chromatography, nuclear magnetic resonance spectroscopy and so on.
Some of the chemical methods have already been discussed in earlier
volumes of Comprehensive Analytical Chemistry. Thus, a short, mainly a
practical survey of qualitative organic analytical methods is found in Chapter
V of Volume IA, and quantitative micro-methods in some detail in Chapter
VIII of Volume IIB. A number of separation methods, such as gas, liquid and
ion-exchange chromatography, are discussed in Volume IIA, spectroscopic
instrumentation and diffuse reflectance methods in Volume IV, microwave
spectroscopy and electron microscopy in Volume V, and Volume VI is
devoted entirely to (mainly organic) infrared spectrophotometry. When
writing my text for Comprehensive Analytical Chemistry, I had these volumes
in mind, trying to avoid unnecessary repetition. I was especially careful not to

repeat what has been well described in Volume IIB, restricting the discussion
of elemental and functional group analysis to recent developments only. I also
avoided theoretical or practical aspects of the instrumental techniques
mentioned, emphasizing only those details which are relevant to the
particular case under discussion. References to the literature are given at the
end of each chapter. Most of these are dated post-1960 to cover recent
developments, the earlier literature being well listed in Chapter VIII of
Volume IIB.
I wish to acknowledge the assistance of my co-workers, who were helpful in
testing some of the methods in the laboratory and in surveying the literature.
Thanks are also due to Elsevier Scientific Publishing Company and the
printers of the Publishing House of the Hungarian Academy of Sciences for
their efforts in producing this volume.
Budapest, August, 1982
xxu

Laszlo Mazor


www.pdfgrip.com

Chapter 1

Introduction. Methods for
of organic compounds

recognition

Both physical and chemical methods are employed in the identification of
organic compounds. The word "identification" may be used in two senses:

identification through comparison with a known substance, and
identification through recognition of the composition and structure of a
compound unknown earlier. In the latter case, the substance must be
examined in detail, all physical and chemical properties must be determined,
while identification through comparison may require one or two of these data
only. In identification work on unknown substances, quantitative analysis
and special techniques, such as UV and IR, N M R and ESR spectroscopy, etc.,
may be necessary, however, they do not supersede chemical analysis methods.
The course and methods of identification and recognition of an unknown
organic substance are shown in Table 1.
The identification of organic compounds with authentic samples becomes
more difficult when the molecular weight of the compound is high, and when a
distinction between compounds with similar structures and molecular
weights (e.g., isomers) must be made.
Organic chemists have dealt with the identification of organic compounds
by means of chemical reactions for many years. One of the first researchers
was H. SchifT, who reported a sensitive reaction suitable for the identification
of urea in 1859. However, in the early days, only few really specific reactions
were known, most being suitable only for the detection of a given group of
compounds (e.g., alkaloids). Intuition often helped the recognition of new
reactions, and the mechanisms of some of them are still not properly
understood. Systematic research work started only in the 1930s, with a
knowledge of the chemical properties of the compound to be detected and the
reagent, and a presumed course of the reaction. In this field, Feigl [1]
developed the method of spot test analysis, and also achieved outstanding
3

3



www.pdfgrip.com

TABLE 1
Qassification of organic chemical analysis
(Separation if the material is not homogeneous)

QUALITATIVE ANALYSIS

QUANTITATIVE ANALYSIS

Preliminary test

CHEMICAL

PHYSICAL

TESTS

TESTS

ELEMENTAL
ANALYSIS

GROUP
ANALYSIS

Chemical
methods
formulae


Chemical Physical
met lods

I
Elemental
analysis.
Group
analysis

Physical
constants.
Spectral
analysis

Literary survey

Determination of structure

Analysis of
derivatives
Identification
tests
(recognition of
identity)

Determination of structure
(identification
of structure)
Sometimes only
some physical

methods, e.g. NMR.

results in the development of specific reactions and in the elucidation of
reaction mechanisms. Today there are specific microreactions available that
make possible the detection of characteristic functional groups or the
substance itself in 0.1-1 jig samples by means of spot tests on slides or on filterpaper. The reagents may be either inorganic or organic. The disadvantage of
organic reagents is that reactions between different organic compounds are
usually slower and less complete than reactions between ions or between
organic compounds and ions. This difficulty led to attempts to decompose
first the organic compounds of higher molecular weight, which are insoluble
4


www.pdfgrip.com

in water, by applying thermal energy or oxidizing or reducing agents, in order
to obtain simple water-soluble or volatile simple inorganic substances (acids,
ammonia, hydrogen sulphide, sulphur dioxide, etc.) or organic substances
(e.g., aldehydes) that can be detected easily and sensitively. These compounds
can also be converted by oxidation or reduction or with appropriate reagents
in such a way that the product can be detected in the reaction mixture
specifically and without interference.
Instrumental methods have gained increasing importance in organic
qualitative analysis. Infrared spectrophotometry and gas chromatography
make possible the detection of not only the functional group but also the
entire structures of complex molecules. The work is easier when standard
compounds are also available and the spectra and chromatograms of the
sample and the reference substance can be compared directly. However,
useful information can often be obtained from the appearance of bands
characteristic of certain functional groups or bonds in the IR spectra, or from

retention indices when using gas chromatography. With homologous series of
compounds, Kovats retention indices can be used for identification purposes.
The IR spectra can be compared with literature data and accurate
identification is possible on the basis of the "fingerprint" pattern. Pyrolysis gas
chromatography and reaction gas chromatography provide possibilities not
only for more accurate identification through decomposition or conversion of
complex molecules, but also for the establishment of the composition of
mixtures from the results.
Even higher performance is offered by mass spectrometry owing to its
much higher resolution. The most modern technique, gas chromatography
combined with mass spectrometry, is employed in the determination of the
structures of complex molecules and the compositions of mixtures.
The identification of a homogeneous pure organic substance is relatively
simple by applying either chemical or instrumental methods. However, the
analysis of mixtures of organic compounds and the identification of the
constituents is much more difficult and may be almost insoluble. In almost all
instances preliminary separation is necessary, as it is rarely possible that the
components of a mixture (even with binary mixtures) can i>e detected
specifically in the presence of each other. When a large amount of sample is
available, separation can be carried out by, e.g., fractional crystallization,
sublimation, distillation, steam distillation or extraction; as quantitative
separation is not necessary, only small amounts of pure fractions need to be
obtained. In suitable micro-scale apparatus these simple separation operations can be accomplished with a few milligrams of sample.
Today, in the separation of organic compounds for qualitative analytical
purposes, paper, thin-layer and ion-exchange chromatographic techniques
3*

5



www.pdfgrip.com

predominate. The suitable choice of the paper or layer material and developing
mixtures to ensure optimal separations, and the use of the most sensitive
detection reactions, make possible the identification of compounds with very
similar chemical and physical properties in multicomponent mixtures. The
relative retention often offers useful information, but a more reliable method is
to effect simultaneous development of an authentic substance.
Column, liquid and ion exchange chromatography are less important in
qualitative analysis, and gel chromatography and ultracentrifugation are
suitable primarily for the separation of high-molecular-weight biological
substances and polymers.
Systematic analysis of organic compounds should also be discussed here.
Starting with the work of H. Staudinger, many attempts have been made to
develop systematic analytical procedures for the identification of unknown
organic substances similar to the system elaborated for particular groups of
and elements in inorganic compounds. However, owing to the fundamental
difference in the nature of organic and inorganic compounds, such a system
with general applicability could not be worked out. The best known and most
widely used procedure was described by R. L. Shriner, R. C. Fuson and D. Y.
Curtin in their book "The Systematic Identification of Organic Compounds",
published in 1956. The method consists of the following steps:
1. Preliminary tests;
2. Determination of physical constants;
3. Detection of elements in the c o m p o u n d ;
4. Detection of functional groups by chemical and spectroscopic methods;
5. Checking literature d a t a ;
6. Preparation and examination of derivatives.
Experts in organic chemistry and organic chemical analysis need not, of
course, follow the steps listed above in all instances when an unknown organic

substance is to be identified, as one or two of the tests will often provide firm
evidence of the identity of the compound. However, the above tests cannot be
applied routinely like the tests in inorganic analysis, and careful consideration
of the individual results is necessary. Any method may be useful and none
should be regarded as out-of-fashion and, except for spectroscopic techniques, all of them will be dealt with in the first part of this book.
A very practical although less systematic survey of qualitative organic
chemical analysis was given in Volume IA of CAC (In: Wilson and Wilson's
series: McGookin) [2] where, in addition to the preliminary tests and
detection methods for elements and functional groups, specific reactions and
the use of derivatives for identification purposes are also reported on the basis
of literature data published up to 1957.
6


www.pdfgrip.com

Chapter 2

Preliminary

tests, identification

of organic

compounds by sensory tests, simple

physical

and chemical methods, and on the basis
of thermal decomposition


products

It is possible to obtain some information on a sample simply by observing
its appearance. This is easier with inorganic substances, as certain inorganic
ions [copper(II), chromium(III), chromium(IV), etc.] have characteristic
colours, and some compounds have characteristic crystal forms (sodium
chloride, alums), whereas most organic compounds are colourless liquids or
white powders. Literature data regarding the crystal forms may be available,
but polymorphism often occurs. Several compounds have different crystal
forms when crystallized from different solvents, and heating may also give rise
to such changes (e.g., diethylbarbituric acid). Here not the crystal form itself,
but the change brought about by thermal action or by the use of another
solvent may be characteristic.
The density of liquids may also be a characteristic property, often without
instrumental determination of its actual value, as the mobility, viscosity,
foaming, etc., of liquids are related to density. The crystal forms can be
observed under a microscope and the information obtained may be useful,
but only when the solvent or solvent mixture used for crystallization is also
known. For example, 2,7-dihydroxynaphthalene is obtained as needles from
water or aqueous ethanol, whereas plates appear on crystallization from
glacial acetic acid. However, when solutions of the same concentration ( 1 2%) and volume (0.02-0.05 c m ) are allowed to evaporate to dryness on equal
areas on a microscope slide under appropriate identical conditions, the shape
of the crystals formed can provide some information regarding the type of
substance involved.
Several different compounds crystallize in the same form from the same
solvent. This isomorphism can be eliminated by the use of solvent mixtures
with suitable variations of the components and their concentration.
Misleading information can be obtained if polymorphism occurs; therefore,
3


7


www.pdfgrip.com

when such an occurrence is suspected, the substance in question should be
repeatedly crystallized (preferably under identical conditions) until the most
stable crystal form is obtained. A more effective method is to increase the
number of components in the solvent mixture used.
The microcrystallized product can be used for further physical and
chemical tests. In examining the crystals, a polarizing microscope is useful:
the picture obtained with crossed Nicols is often very characteristic.
The so-called microcrystal test is based on the fact that certain compounds
form precipitates with characteristic crystals' shape on addition of appropriate reagents. This is a very old method and can be regarded as one of the first
tests in qualitative organic microanalysis. Several systematic procedures have
been developed for the recognition of certain compound groups (e.g.,
alkaloids). Most recently, Fulton [3] has dealt with this method and
described microcrystal tests for 159 organic compounds, mainly drugs and
drug precursors.
The microcrystals obtained in this test were divided into nine groups by
Fulton on the basis of the shape of crystals, the direction of growth,
aggregation phenomena, the manner of branching of crystal aggregates, etc.
In this system, 25 reagents are applied (acids, bases, complex salts, etc.) and
the reactions taking place are divided into nine groups.
This procedure is actually a chemical method similar to the spot tests
suitable for the detection of elemental constituents and functional groups in
organic compounds. The difference is that in the microcrystal test the
reactions are carried out on a microscope slide and the result is observed with
a microscope of 30-50-fold magnification. In contrast to spot tests, which will

be dealt with at length in the chapter devoted to qualitative chemical analysis,
the microcrystal test also makes use of the crystal shape, but identification is
based exclusively on this feature and is somewhat uncertain because of other
phenomena following crystallization.
Organic compounds, unlike inorganic c o m p o u n d s may have very
characteristic odours, usually indicating the group of compounds to which
the substance belongs. Some groups of compounds with characteristic odour
are listed in Table 2.
The smell of liquids is enhanced by heating, and the smell of solids will also
become more intense when some crystals are rubbed in the hand. There are
compounds and compound groups with characteristic tastes, but such testing
should be avoided, as several substances are toxic even in very small amounts.
It must be emphasized that these sensory tests provide limited information,
which depends strongly on the experience of the observer. Chemists with a
Hmited knowledge of materials cannot make use of these characteristics, and
even for experts they represent initial guidance only.
8


www.pdfgrip.com

TABLE 2.
Some compounds with characteristic smell (according to Linne-Zwaadenaker)
Character of smell

Compound

Ether-type
Aromatic, almond smell
Aromatic, camphor smell

Aromatic, lemon smell
Balsamic, flower smell
Balsamic, lily smell
Balsamic, vanillin smell
Musk smell
Garlic smell
Cacodyl oxide smell
Tar smell

Ethyl acetate, ethanol, acetone, amyl acetate
Nitrobenzene, benzaldehyde, benzonitrile
Camphor, thymol, saffrole, eugenol, carvacrol
Citral, linalol acetate
Methyl anthranilate, terpineol
Heliotropine (piperonal), styrene
Vanillin, anisaldehyde
Muscone, trinitroisobutyltoluene
Ethyl sulphide
Cacodyl, trimethylamine
Isobutanol, aniline, p-isopropylaniline, benzene, cresol, guaiacol
Valeric acid, capric acid, methyl heptyl ketone
Pyridine
Indole, scatole

Rancid smell
Narcotic smell
Foul smell

Organic compounds are usually insoluble in water, some are slightly
soluble in water and readily soluble in alcohols, while most are soluble mainly

in apolar solvents. The dissolution of liquids in liquids, that is, mixing, may
also be characteristic, but much more apolar liquids than solids can be
dissolved in or mixed with water and alcohols.
Dissolution of organic compounds in organic solvents is often not merely a
simple physical process, but a certain interaction occurs between the
molecules of the solute and the solvent; even chemical reactions can take
place. As a result of this interaction, the molecules of the solvent in the vicinity
of the solute molecules may possess properties different from those in the bulk
of liquid. For example, a strongly polar solute exerts a polarizing action on
the solvent molecules in its vicinity. The solvent may facilitate reactions
between solutes, and therefore the solvent cannot always be regarded simply
as an inert medium.
In view of these facts, the earlier classification of solvents (polar and apolar)
should be replaced by another system (Table 3):
1. Protic solvents;
2. Apolar or less aprotic solvents;
3. Dipolar aprotic solvents.
Of the protic solvents, the most important are water, alcohols, amines and
carboxylic acids. The second group consists of hydrocarbons, chlorinated
9


www.pdfgrip.com

TABLE 3.
Physical constants of some solvents
Solvent
Protic solvents:
Water
Methanol

Ethanol
Glycerol
Acetic acid
Form amide
Apolar or less polar aprotic
Carbon tetrachloride
Benzene
Dioxane
Chloroform
Diethyl ether
Pyridine
Tetrahydrofuran
Dipolar aprotic solvents:
Acetone
Acetaldehyde
Acetonitrile
Nitrobenzene
Nitromethane
Dimethylformamide
Dimethylacetamide
Dimethyl sulphoxide
Hexamethylphosphoramide

Melting point Boiling point

Relative
permittivity

0.0
-97.8

-114.6
18.2
16.6
2.55

100
64.65
78.37
290
118.1
105(11)

80.1
33.7
25.8
43.0
6.17
113.5

-22.8
5.51
11.8
-63.5
-116.3
-42
-108.5

76.8
80.1
101.4

61.3
34.6
115.3
65.5

2.236
2.283
2.235
4.813
4.35
12.3
7.89

-95
-123.5
-45.7
5.7
-28.4
-61
20.2
6

56.2
20.2
81.6
210.9
101.3
153
165
189

100 (6)

20.7
21.6
27.5
34.8
35.9
37.2
37.8
46.6
30.0

1 8

20

2 0

2 0

20

15

solvents:

-

20


20

20

20

20

25

25

25

20

2 0

25

25

2 0

25

25

25


hydrocarbons, benzene, dioxane and pyridine. The most important solvents
in G r o u p 3 are acetone, nitrobenzene, nitromethane and dimethylformamide.
Protic solvents (Group 1) possess both nucleophilic and electrophilic
properties. In these solvents the anions are strongly solvated and the mobile
hydrogen atoms of these solvents are often capable of forming hydrogen
bonds. For example, with the bromide ion we have:
-de

R

O

H

6®

Br..... H

d®

—be

O

R

As these solvents have a lone pair of electrons and thus electron-donating
ability, cations can also be solvated by them:

IOI

H

10

.

/

Na .

IOI

+

R

H


www.pdfgrip.com

When such solvents also have a high permittivity (water, formamide), they
greatly facilitate spontaneous ionization, that is, S 1 reactions. The solvent
molecules usually form associates through hydrogen bonds.
Solvents in G r o u p 2 have relatively low dielectric constants. Some of them,
e.g., diethyl ether, dioxane and tetrahydrofuran, are strongly nucleophilic.
The solvents in G r o u p 3 have relatively high permittivity. In dissolution
reactions these behave like those in G r o u p 2, but ion aggregates are formed to
a lower extent in comparison with solvents with lower permittivities (less than
15). F r o m the practical point of view, acetone, dimethylformamide,

dimethylacetamide and dimethyl sulphoxide are the most important
solvents; they are miscible with water. Both strongly and weakly nucleophilic
solvents (dimethyl sulphoxide and acetonitrile, respectively) appear in this
group.
For inorganic ions, by the middle of the last century a system had already
been developed and used in which different reagents made possible the
precipitation and complete separation of inorganic ions (e.g., the Fresenius
method for separation of cations as sulphides). Later attempts were made to
develop a similar system for the grouping and separation of organic
compounds. At that time, sufficient knowledge had been gathered on the
easily determined properties of organic compounds (volatility, solubilities in
different solvents, etc.). However, owing to the rapid increase in the number of
known organic compounds, these trials, which had seemed to be successful at
first, lost their importance. In practice, the most modern methods can still be
useful when an unknown organic substance is to be identified, but should be
regarded as informatory data and preliminary tests only.
At the beginning of the twentieth century, Th. Mullikan and H. Staudinger
developed almost simultaneously a "solubility system" which has been used
up to the present time without substantial modifications. The latest edition of
Staudinger's book, modernized and supplemented, was published in 1968.
Staudinger classified organic compounds according to their melting point,
volatility (boiling point) and solubility, regarded as physical characteristics
related to molecular weight. With respect to volatility, the limiting
temperature is 160°C. At lower temperatures compounds can be distilled
without decomposition (in some instances, distillation is carried out at
reduced pressure). Measurement of the melting point and boiling point and
their comparison with literature data provide useful information for
identification. However, neither of these data are suitable for use in the
classification of organic compounds, as they are hardly related to their
chemical properties.

The solubility of a substance in certain solvents and reagents is more
suitable for classification purposes because, as discussed in connection with
N

11


www.pdfgrip.com

the mechanism of dissolution, this may indicate the chemical properties of a
given compound.
O n the basis of solubility, Staudinger divided organic compounds into the
following five groups (today this system is obsolete and is primarily of
historical importance):
1. C o m p o u n d s soluble in diethyl ether and insoluble in water. As the
permittivity of diethyl ether is low (4.35), it belongs to the less polar aprotic
solvent group, and therefore a larger number of compounds are soluble in it
than in solvents with definitely apolar character, such as carbon tetrachloride
and benzene. Several solvents with similarly low relative permittivities are
known (chloroform, dioxane, etc.), but diethyl ether was preferred because of
its easy removal after the test, which allows the the same sample to be used in
further examinations. According to Staudinger, compounds soluble in diethyl
ether and insoluble in water are definitely organic in character.
2. C o m p o u n d s soluble in both diethyl ether and water. These are called
compounds of mixed organic-inorganic nature. The permittivity of water and
diethyl ether differ greatly, the mechanisms of their dissolution are also
different, and ionization may occur in water. The relative permittivities of two
frequently used alcohols, methanol (33.7) and ethanol (25.8), lie between
those of water and diethyl ether. They can dissolve most compounds with
"clearly organic character" in G r o u p 1 and also certain salts, and are

particularly good solvents for compounds containing hydroxyl group(s).
3. C o m p o u n d s soluble in water and insoluble in diethyl ether. These are
organic substances with a somewhat inorganic character. Primarily salts of
low-molecular-weight organic acids belong to this group, and are limited in
number.
4. Compounds insoluble in both diethyl ether and water. This group
consists of high-molecular-weight organic compounds, such as polycarboxylic acids, acid amides with an otherwise mixed organic-inorganic character
and insoluble salts (e.g., alkaline earth metal and other metal salts of organic
acids), which can be regarded as inorganic compounds, irrespective of their
solubility.
5. There are some groups of compounds that are soluble in diethyl ether,
which fundamentally belong to G r o u p 1, but which undergo decomposition
in water. This group includes acid halides and isocyanates.
The members of the above five groups may be volatile, like the lowmolecular-weight compounds in G r o u p s 1, 2 and 5, or non-volatile (or
volatilized only after decomposition), which are usually compounds with
higher molecular weight in any of the five groups.
With compounds that are soluble in diethyl ether, further information can
be obtained after the simple dissolution test by use of so-called reactive
12


www.pdfgrip.com

solvents. An example is 5% hydrochloric acid, which dissolves basic
substances, such as amines, with the formation of hydrochlorides.
C o m p o u n d s with acidic character are soluble in 5% sodium hydroxide or
5% sodium hydrogen carbonate solutions while forming salts. Organic acids,
mainly those of low molecular weight with acid dissociation constants higher
than that of carbonic acid (4.3 x 1 0 " ) (e.g., acetic acid, 1.7 x 1 0 " ) undergo
dissolution while releasing carbon dioxide. Weaker acids, with acid

dissociation constants higher than the second acid dissociation constant of
carbonic acid (5.6 x 1 0 " ) are dissolved without the formation of carbon
dioxide, like diethylbarbituric acid (3.7 x 1 0 ~ ) . Even weaker acids, if their
sodium salts are soluble in water, are dissolved in 5% sodium hydroxide
solution, which, of course, also dissolves the stronger acids. When a freshly
prepared solution of 5% sodium hydrogen carbonate is made pale pink with
one d r o p of phenolphthalein, the colour disappears under the influence of
weak acids, whereas it becomes enhanced in the presence of basic compounds.
If the sample is soluble in water or water-alcohol (1:1), the reaction of the
solution can be checked with a universal indicator solution or a p H indicator
paper, and this can indicate the group to which the compound in question
belongs.
Neutral compounds, insoluble in water, and therefore insoluble in acids
and bases also, can further be tested with concentrated sulphuric acid. If the
substance dissolves in it, a simple dissolution process explainable by the high
permittivity of concentrated sulphuric acid (84.0) or sulphonation of the
substance can be considered. If the substance is soluble in concentrated
sulphuric acid, the solution tests are continued with concentrated orthophosphoric acid, which also has a high permittivity. This is the most suitable
solvent for alcohols with less than nine carbon atoms, aldehydes, methyl
ketones, alicyclic ketones and esters. Similar compounds with more than nine
carbon atoms and also quinones and unsaturated hydrocarbons, are
insoluble in this reagent.
Saturated aliphatic hydrocarbons, aromatic hydrocarbons and their
halogen derivatives are insoluble in both concentrated sulphuric acid and
orthophosphoric acid.
There are compounds that to not fit into either of the groups discussed
above, e.g., nitro compounds, amides, negatively substituted amines, nitriles,
azo compounds, hydrazo compounds, sulphones, thiols and thioethers. All of
these compounds contain nitrogen or sulphur atoms.
Heating and combustion tests. The most simple means of ensuring that a

sample is an organic substance is to heat it with concentrated sulphuric acid
or chromic acid [ 4 ] . Organic substances turn black under the influence of
7

5

1 1

8

13


www.pdfgrip.com

concentrated sulphuric acid, or turn the yellow colour of chromic acid
mixture green, owing to the reduction of chromium(VI) ions.
The thermal decomposition of several organic compounds yields compounds with lower molecular weight and characteristic chemical properties.
These may be inorganic (hydrogen sulphide, hydrogen cyanide, etc.) or
organic compounds (formaldehyde, acetaldehyde, methanol, acetic acid, etc.).
The same compound may give different decomposition products when heated
under oxidizing or reducing conditions. For example, sulphur-containing
compounds may release hydrogen sulphide or sulphur dioxide when heated
under reducing or oxidizing conditions, respectively. Certain compounds
undergo decomposition with the formation of volatile aldehydes or acids, and
these decomposition products can be detected in the vapour by means of
simple reactions. Detectable decomposition products of some compounds are
shown in Table 4.
In the heating test the sample is placed in a narrow test-tube, the open end
of which is covered with paper impregnated with a suitable reagent, then

heating is cautiously started. Reducing conditions are ensured by the carbon
TABLE 4.
Characteristic products from reductive pyrolysis of some organic compounds
Compound
Alloxantine
Aminophylline
Barbituric acid
Benzidine
Biuret
Zinconine
Cistine
Dimethylglyoxime
p, p'-Diaminodiphenyl sulfone
Glucose
Guanidine carbonate
Hydrazobenzene
Uric acid
D, L-Isoleucine
1 -Naphthylamine. HC1
Nitrozo-R salt
6-Nitroquinoline
Poly(vinyl alcohol)
Rhodamine-B
Saccharin
Thiourea
Xanthopterine

14

Product

Acid

Alkaline H C N

(CN)

+

+
+
+
+
+

+
+
+
+
+

+
+

-

-

+

-


+
+

-

+

-

+
+
+
+
+

-

+

+

+

-

+

-


+

-

+
+
+

2

Reducing

H S

CH CHO

-

-

-

2

—

—

—


-

+

-

-

+
+

-

-

-

+
+

-

+

-

+

+
+

+
+
+
+

-

+

-

+
+

+
+
+
+

+

-

-

-

+

-


+

+

-

-

+
+
+

+
+

-

3

—

+

-

+
+

-



www.pdfgrip.com

and hydrogen contents of the substance. Air can be expelled from the test-tube
with an inert gas prior to starting the test.
T h e ignition test is carried out as follows. About 30-50 mg of sample are
placed on the end of a narrow porcelain plate, then this end is moved slowly
towards the small, colourless flame of a micro burner. Under the influence of
heat, certain substances undergo sublimation or vaporization, and the
vapours are ignited in the flame. In this way, compounds with high carbon
and low oxygen contents can be clearly recognized, as their vapours make the
flame strongly luminous and sooty. Almost all aromatic compounds show
this behaviour. Compounds with low carbon content, relatively rich in
oxygen (mainly aliphatic compounds except for high-molecular-weight
hydrocarbons) produce a slightly luminous or colourless flame. Some
substances swell on heating, then undergo melting and boiling; they usually
contain water of crystallization. Others exhibit explosion-like phenomena
during burning, such as nitro compounds. Polyhalogenated compounds burn
only slightly or not at all. The odour of combustion products can be very
characteristic; sugars have a caramel smell, and proteins give off a smell of
burning hair. However, these smells are not given by all carbohydrates and
amino compounds, and all such sensory observations can be very misleading
without a thorough knowledge of the materials involved.
Preliminary tests with mixtures. With liquid or powder mixtures (e.g., drug
formulations) the preliminary tests reviewed above are less promising than
with homogeneous substances but, in favourable situations when only twoor three-component mixtures are involved, they can still be applied. With
liquid mixtures, when not starting directly with fractional distillation,
qualitative evaporation tests can be carried out. A few drops of the liquid are
heated on a watch-glass and, if the boiling points of the components are

significantly different, this fact can be observed. If a solid residue is obtained,
the sample was, in fact, a solution.
Solubility tests with powder mixtures can be accomplished in a conical
test-tube with 0.1 c m divisions. When two or more components are present
in similar amounts, the decrease in the amount of sedimenting non-dissolved
material can be noted. The test is repeated with the residue using another
solvent, and the solubilities of two or more components in various solvents
can be established.
With powder mixtures, heating tests can provide useful information when
the decomposition products of the constituents are different. The reagent
paper covering the open end of the test-tube is replaced with another while
increasing the temperature further.
Differences in the behaviour of gases evolved from components that have
different decomposition temperatures can also be observed during the
3

15


www.pdfgrip.com

ignition test. As in this instance a uniform rate of heating cannot be ensured,
subsequent phenomena characteristic of the individual components can be
observed only when the decomposition temperatures are greatly different.
When these tests d o not yield unambiguous information, it is better to turn
to simple separation methods on the micro- or semimicro-scale, such as
distillation, extraction and sublimation. Preliminary studies on the components separated qualitatively are recommended prior to starting systematic
analysis.
The information obtainable from preliminary tests may provide valuable
help, but it should be stressed that simple separation methods are rarely

complete and the products should be regarded as contaminated even in the
preliminary tests.
Thermo-micro technique. When discussing the preliminary tests, it was
mentioned that organic compounds often undergo characteristic changes
during heating. In the course of the heating and ignition tests, the thermal
decomposition products are identified by sensing or simple chemical
reactions. These methods are regarded as preliminary tests, as they are rather
uncertain and the same phenomenon or reaction may be obtained with
several different compounds. Several tenths of a gram of sample are required
for these examinations.
With the development of Koflers' hot-stage microscope a new testing
technique called the "thermomicro method" become available. This is not
only suitable for the determination of certain physical constants (melting
point, molecular weight, refractivity, etc.), but also several important
conclusions can be drawn from the behaviour of the crystals of organic
compounds during heating to the melting point, which also facilitates or
supports identification. F o r this purpose, only a few micrograms of sample are
required.
According to the above description, thermomicro methods are those in
which the behaviour of milligram amounts of a sample are studied as a
function of temperature in order to obtain information regarding the nature
of the substance. They are suitable for the determination of physical constants
also, but this aspect will be discussed in detail in Chapter 4.
Changes in modification. It is well known that substances with identical
chemical properties can take different crystal forms. For example, elemental
sulphur can exist in three modifications at different temperatures. The
conversion into the opposite direction during cooling is slow, and the crystal
forms stable at higher temperatures can exist for long periods (sometimes
several years) in the metastable state. This phenomenon of polymorphism
and its temperature dependence also occur with organic compounds, in fact

more frequently than with elements and inorganic compounds.
16