Analytical Chemistry of Polycyclic Aromatic Compounds

467 Pages·1981·6.29 MB·English

by  Milton Lee (Auth.)

Analytical Chemistry
of P o l y c y c l ic
A r o m a t ic C o m p o u n ds
M I L T ON L. L EE
Department of Chemistry
Brigham Young University
Provo, Utah
M I L OS V. N O V O T NY
Department of Chemistry
Indiana University
Bloomington, Indiana
K E I TH D. B A R T LE
Department of Physical Chemistry
University of Leeds
Leeds, United Kingdom
1981
ACADEMIC PRESS
A Subsidiary of Harcourt Brace Jovanovich, Publishers
New York London Toronto Sydney San Francisco
Copyright © 1981, by Academic Press, Inc.
all rights reserved.
no part of this publication may be reproduced or
transmitted in any form or by any means, electronic
or mechanical, including photocopy, recording, or any
information storage and retrieval system, without
permission in writing from the publisher.
ACADEMIC PRESS, INC.
Ill Fifth Avenue, New York, New York 10003
United Kingdom Edition published by
ACADEMIC PRESS, INC. (LONDON) LTD.
24/28 Oval Road, London NW1 7DX
Library of Congress Cataloging in Publication Data
Lee, Milton L.
Analytical chemistry of polycyclic aromatic compounds.
Includes bibliographical references and index.
1. Polycyclic compounds—Analysis. 2. Aromatic
compounds—Analysis. I. Novotny, Milos, Date.
II. Bartle, Keith D. III. Title.
Q0335.L48 547».5 80-68559
ISBN 0-12-440840-0
PRINTED IN THE UNITED STATES OF AMERICA
81 82 83 84 9 8 7 6 5 4 3 2 1
Preface
ΤΓ
HE RAPID GROWTH in industry over the last century and particularly
within the last several decades has required more critical evaluations
of environmental health hazards associated with combustion products
and effluents from these industries. The recent increase in the utiliza­
tion of coal and other synthetic fuels to meet changing world energy
demands places even greater emphasis on these evaluations. Fortu­
nately, developments in analytical methodology and instrumentation
have largely paralleled industrial growth, and many of the chemical
factors relating to the environment have been identified. Among these
are the polycyclic aromatic compounds, the largest class of chemical
carcinogens known today.
The carcinogenic and mutagenic properties of numerous polycyclic
compounds have been documented, and many others are presently
under investigation. The modern age of chemical instrumentation has
already had a significant impact in areas related to this class of com­
pounds: environmental toxicology, experimental carcinogenesis, en­
vironmental chemistry, chemical and fuels engineering, etc. The known
health hazards associated with the increasing emission of polycyclic
aromatic compounds into our environment, along with the develop­
ing societal environmental awareness dictate the need for both further
structural identification and more accurate and precise quantitative
measurement of these substances.
Although many excellent books have been written on various aspects
of carcinogenesis, and although both biological and chemical proper­
ties of polycyclic aromatic compounds have been discussed at many
international symposia, it is our belief that such important subjects
ix
χ Preface
as the chemical separation, the structural identification, and the quan­
titative measurement of these compounds had not been drawn together
and treated in a comprehensive manner.
This book is mainly devoted to the discussion and critical evaluation
of various chromatographic (Chapters 5-7) and spectroscopic (Chap­
ters 8-10) methods. It is shown how gas chromatography and high-
performance liquid chromatography can be both competitive and
complementary analytical methods. Ancillary techniques of both are
emphasized for the structural elucidation of individual polycyclic
aromatic compounds in complex mixtures. The merits of spectroscopic
methods in both structural work and quantitation are compared. New
directions for these analytical techniques are also discussed.
Chapters 1-3 are descriptive in nature and provide the reader with
background information concerning the chemistry, occurrence, and
toxicology of polycyclic aromatic compounds. These chapters were
included to give the reader basic information pertinent to the under­
standing and appreciation of the analytical chemistry of these com­
pounds.
The isolation of polycyclic aromatic compounds from a wide variety
of materials and matrices necessitates a number of different ap­
proaches; and therefore sample collection, extraction, separation, and
purification are discussed in Chapter 4. Numerous methods and
examples which cover most applications are discussed.
An important point stressed in this book is that no one analytical
technique is sufficient to solve all analytical problems associated with
this class of compounds; and that therefore, various multi-technique
approaches are required. This is demonstrated in Chapter 11 with two
practical examples representative of the widely differing problems that
may be encountered. This book does not pretend to have the universal
analytical solution to all studies involving polycyclic aromatic com­
pounds. Instead, the different analytical techniques and approaches
are treated in some detail in separate sections and their advantages and
disadvantages explained. It is hoped that sufficient information is pro­
vided concerning the chemical and physical properties of the polycyclic
aromatic compounds as well as the principles behind the various
analytical techniques so that the reader can approach any particular
analytical problem with sufficient understanding. The correct nomen­
clature of the polycyclic aromatic compounds is contained in the
appendices, and should provide a valuable resource for those new to
this class of compounds.
Preface xi
This book is recommended to all scientists involved with the study
of polycyclic aromatic compounds, to analysts who need to acquire
routine data, as well as to individuals charged with formulating en­
vironmental policies and drafting regulations. In addition, this book
may also be appreciated by engineers concerned with emission-control
and energy-related industries.
The timely completion of this book was aided by fellow scientists
who gave permission to reproduce their data and who often provided
as yet unpublished manuscripts and valuable criticisms. We would
also like to thank Mary Fencl, Paul Peaden, Dan Vassilaros, Cherylyn
Willey, and Bob Wright, for valuable help in assembling and proof­
reading the text, compiling the information in the appendices, and
preparing the figures for reproduction. The untiring assistance of Ms.
Peggy Gore is gratefully acknowledged for typing and retyping the
text, and for invaluable assistance in the preparation of the manu­
script. Finally, we are grateful to our families who gave the necessary
encouragement and provided an atmosphere conducive for us to initiate
and complete this book.
Milton L. Lee
Milos Novotny
Keith D. Bartle
1
Physical and Chemical Properties
I. NOMENCLATURE
Polycyclic aromatic compounds (PAC) have been studied for well over a
century, and during this time many compounds have been named unsys-
tematically. Some names reflect the initial isolation of compounds from coal
tar (naphthalene, pyrene, etc.); some reflect their color (fluoranthene and
chrysene—the latter erroneously, because of contamination with naph-
thacene which is orange); and some reflect the shape of their molecules
(coronene, ovalene). Such names passed into general use, and it proved
impractical to change them when systematic nomenclature was introduced.
Thus, many important PAC systems are named nonsystematically.
Recently, IUPAC (International Union of Pure and Applied Chemistry)
attempted to systematize PAC nomenclature, prefixing to the name of a
parent ring system the names of other component parts (7). Appendices 1
through 4 list the names and structures of many of the hydrocarbons and
their heterocyclic analogs discussed in the remainder of the book. An
exhaustive list of PAC is contained in "The Ring Index" (2). All the ring
systems used in organic chemistry are classified according to the number and
identity of the atoms in each ring and are named and numbered.
The numbering and names of the compounds in Appendices 1-4 are based
on the following rules:
1. Rings are drawn with two sides vertical wherever possible.
2. Irrespective of their size, as many rings as possible are drawn in a
horizontal line.
3. As much as possible of the rest of the structure is arranged in the top
right quadrant and as little as possible in the bottom left quadrant (the middle
of the first row is taken as the center of the circle).
ι
2 1. Physical and Chemical Properties
4. Starting with the first carbon atom not engaged in ring fusion in the
right-hand ring of the top row, numbering proceeds clockwise around the
molecule (anthracene and phenanthrene are exceptions).
5. Atoms engaged in ring fusion are given the letters a, b, c, etc., after
the number of the preceding atom, e.g., triphenylene (1):
2
(I)
6. Certain trivial names are retained. Otherwise the name of a fused-ring
system is made up of a prefix of the fixed part (benzo, cyclopenta, or a group
of rings such as indeno—see abbreviations listed in Appendix 1) followed
by an italic letter or letters denoting the bond or bonds of the base (which
has as many rings as possible) at which fusion occurs, a refers to the 1,2-bond,
and all bonds are then lettered sequentially whether or not they carry hy­
drogen atoms; the name of the parent compound follows. Examples are
benz[#]anthracene (2) and 4i/-cyclopenta[ife/]phenanthrene (3).
(2) (3)
If more than one ring is fused, the italic letters are separated by a comma,
e.g., dibenz[<z,c]anthracene (4).
(4)
The fusion position on the first ring system is shown, if necessary, by the
appropriate numeral which precedes the italic letters, e.g., indeno[l,2,3-cd]-
pyrene (5).
II. Physical Properties 3
(5)
7. A component CH of a ring is indicated by the italic Η preceded by
2
the appropriate numeral, except where its position is assumed, as for exam­
ple in the compounds trivially named indene and fluorene (Appendix 1),
e.g., l/f-benz[tffe]anthracene (6). Where there is a choice, the carbon atom
carrying an indicated hydrogen atom is numbered as low as possible.
(6)
8. Hydrogenation is denoted by prefixes such as dihydro, etc., followed
by the name of the corresponding unreduced hydrocarbon, e.g., 1,4-dihy-
dronaphthalene (7):
(7)
An even greater variety of structure is presented by the heterocyclic
analogs and derivatives of polycyclic aromatic hydrocarbons (PAH), even
if only compounds containing a single heteroatom are considered (Appen­
dices 2, 3, and 4). Similar rules of nomenclature apply as outlined above,
since, in general, the name is composed of a hydrocarbon ring system followed
by a trivial heterocycle name,. Numbering also follows the rules for hydro­
carbons; where there is a choice of orientation, low numbers are assigned
to heteroatoms. In an alternative IUPAC-approved scheme, heterocyclic
systems may be named by prefixing aza (N), oxa (O), or thio (S) to the name
of the corresponding hydrocarbon: thus benz[#]isoquinoline is named
2-azaanthracene.
II. PHYSICAL PROPERTIES
The physical and spectroscopic properties of PAC are dominated by the
conjugated π-electron systems which also account for their chemical stability.
4 1. Physical and Chemical Properties
All PAC, with the exception of a few hydrogenated derivatives, are solids
at ambient temperatures and are the least volatile of the hydrocarbons. PAC
occur in air, mainly adsorbed on particles (Chapter 2). The boiling points of
PAC are markedly higher than those of the w-alkanes of the same carbon
number. Nonetheless, losses from environmental PAC samples are probable
without stringent precautions (3). Particulates from urban air stored in an
open container, but in the dark, showed the following losses (4): pyrene
88%, benzo[tf]pyrene 32%, benzo[#A/]perylene 10%, but coronene only 1%.
The availability of high-energy π-bonding orbitals and of relatively low-
energy 7i*-antibonding orbitals in PAC leads to the absorption of visible
or ultraviolet (UV) radiation by the transition of an electron from the
the π- to 7r*-orbital which gives characteristic absorption and fluorescence
spectra. The processes occurring when UV or visible light is absorbed by
PAC are illustrated in Fig. 1-1. Excitation Ε takes the molecule from the
ground-state singlet S to the first excited state S. In condensed systems,
0 i
any excess vibrational energy is lost within a picosecond by transfer to neigh­
boring ground-state molecules. From the lowest vibrational level of S the
1
molecule may either: (a) return to the ground-state S by radiationless
0
internal conversion (IC); (b) return to S by fluorescent emission (F); or
0
(c) be converted to the excited vibrational levels of the lowest triplet state
T, and then by very rapid (less than 1 ps) internal conversion (intersystem
x
Fig. 1-1. Electronic energy levels and transitions for PAC.
II. Physical Properties 5
crossing—ISC) go to the lowest vibrational level of T. The lifetime of S
1 x
is short (10-100 ns for PAH), but process (a) above is generally unimportant:
for anthracene in ethanol at 20°C, about 30% of the excited singlet disappears
by the S -+S fluorescence process and 70% by the S ->Τχ process.
x 0 i
Once in the triplet state, the radiative process ^-^So, called phos­
phorescence (P), is slow because the transition involves a change in spin
multiplicity and is "forbidden." Weak phosphorescence is often observed,
however, and the variation with time of the intensity of the phosphorescence
emission may be used to measure the lifetime of the triplet state.
The energy differences between S and S, and therefore the wavelengths
0 x
of exciting radiation, depend on the separations between the various molecu­
lar orbitals. Certain features of their UV/visible spectra thus are common to
all PAC and can be interpreted as follows. The strong absorption bands
designated (5, 6) a, p, and /?, which occur in that order at decreasing wave­
lengths, have extinction coefficients (E ) of generally ~102, 104, and
max
105 M"1 cm" respectively. The p-band is assigned (Fig. 1-2) to transitions
from the highest occupied molecular orbital to the lowest unoccupied molec­
ular orbital, and the a- and /?-bands to transitions from the next highest
occupied to lowest unoccupied molecular orbital, and from the highest
occupied to the next higher unoccupied molecular orbital.
The phenomenon named annellation by Clar may be used (5,6) to explain
why the α-, ρ-, and jS-bands retain their characteristic features while shifting
towards the red with ring number. Briefly, in fused-ring PAH, some rings give
Unoccupied
MOs
bands
Increasing
energy
e-band
Occupied
MOs
Fig. 1-2. Electron transitions corresponding to α-, β-, and p-bands in UV/visible spectra
of PAH.