Atmospheric Oxidation and Antioxidants. Volume I

238 Pages·1993·2.89 MB·English

by  Gerald Scott (Auth.)

Atmospheric
Oxidation and
Antioxidants
VOLUME I
G. Scott, editor
Green Ridge
Newby Nr. Middlesbrough
Cleveland TS8 0AH
U.K.
ELSEVIER
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vii
PREFACE
Oxidation by molecular oxygen is one of the most practically important of
all chemical processes. It is the basis of energy production in animals and,
at the same time, a major cause of irreversible deterioration and ultimate
death. Man uses oxygen positively in the production of energy by combus
tion, and many important industrial processes in the petrochemical in
dustry are based on the controlled oxidation of hydrocarbons. At the same
time, oxidation is the main cause of deterioration of foodstuffs and of many
industrial polymers.
It is clearly of great practical importance that the mechanisms of oxida
tion and its prevention should be understood in order to utilise the reactions
of oxygen more effectively but, equally importantly, to control the adverse
effects of oxygen on man-made products and in biological systems. The three
volumes of this work are directed toward these objectives. Volume I reviews
current understanding of autoxidation, largely on the basis of the reactions
of oxygen with characterised chemicals. From this flows the modern mech
anisms of antioxidant action and their application in stabilisation technol
ogy. Volume II examines the oxidation chemistry of carbon-based materials
in more detail with emphasis on the technological phenomena that result
from the attack of oxygen and the practical procedures developed to prevent
them. Volume III addresses our present understanding of how oxidation is
involved both positively and negatively in life processes. This is a more
recent and rapidly developing aspect of oxidation chemistry and many of the
concepts still have to be proved by rigorous scientific investigation. Never
theless, the mechanistic principles developed as a result of studies in vitro
over the years now provide the basis for understanding the complex oxida
tion chemistry of life processes and its control by biological antioxidants.
The three volumes, although complementary to one another, form a single
whole and it is hoped that, by frequent cross-reference, the reader will be
enabled to utilise ideas and experience from other disciplines to enlighten
his own. The first edition of this work was published a quarter of a century
ago in a single volume. The increase in size of the second edition reflects the
growth of interest in the subject in the intervening period. Nevertheless, the
mechanisms outlined in the first edition still form the basis of our present
understanding of oxidation chemistry and there will therefore be frequent
reference to it in this edition.
GERALD SCOTT
IX
LIST OF AUTHORS
S. AL-MALAIKA (Volume I)
Department of Chemical Engineering and Applied Chemistry, Aston
University, Aston Triangle, Birmingham B4 7ET, U.K.
N.C. BILLINGHAM (Volume II)
School of Chemistry and Molecular Sciences, University of Sussex,
Brighton BN1 9QJ, U.K.
JOHN A. BLAIR (Volume III)
Pharmaceutical Sciences Institute, Aston University, Aston Triangle,
Birmingham B4 7ET, U.K.
E.B. BURLAKOVA (Volume III)
The Institute of Chemical Physics, Kosygin-str. 4, Moscow 117334,
Russia
G. CAMINO (Volume II)
Dipartimento di Chimica Inorganica, Universita Degli Studi di Torino,
Via Pietro Giuria, 10125 Torino, Italy
D.J. CARLSSON (Volume II)
Division of Chemistry, National Research Council of Canada, Ottawa,
K1A 0R9, Canada
T. COLCLOUGH (Volume II)
Exxon Chemical Technology Centre, Abingdon, Oxon. 0X13 6BB, U.K.
NANCY E. DAVIDSON (Volume III)
Oncology Center, Johns Hopkins Medical Institutions, 615 N. Wolfe
Street, Baltimore, MD 21205, U.S.A.
H.H. DRAPER (Volume III)
Department of Nutritional Sciences, University of Guelph, Ontario,
Canada NIG 2W1
X
H. BRIAN DUNFORD (Volume III)
Department of Chemistry, University of Alberta, Edmonton, Alberta,
Canada T6G 2G2
GILL FARRAR (Volume III)
Pharmaceutical Sciences Institute, Aston University, Aston Triangle,
Birmingham B4 7ET, U.K.
JOHN M.C. GUTTERIDGE (Volume III)
National Institute for Biological Standards and Control, Blanche Lane,
South Mimms, Potters Bar, Herts. EN6 3QG, U.K.
KATHRYN Z. GUYTON (Volume III)
Department of Environmental Health Sciences, Johns Hopkins
Medical Institutions, 615 N. Wolfe Street, Baltimore, MD 21205, U.S.A.
BARRY HALLIWELL (Volume III)
Department of Biochemistry, King's College (KQC), Strand Campus,
London WC2R 2LS, U.K.
THOMAS W. KENSLER (Volume III)
Department of Environmental Health Sciences and Department of
Pharmacology and Molecular Sciences, Johns Hopkins Medical
Institutions, 615 N. Wolfe Street, Baltimore, MD 21205, U.S.A.
S.P. KOCHHAR (Volume II)
SPK Consultancy Services, 48 Chiltern Crescent, Earley, Reading RG6
IAN, U.K
R.P. LATTIMER (Volume II)
The B.F. Goodrich Research and Development Center, Brecksville, OH
44141, U.S.A.
R.W. LAYER (Volume II)
The B.F. Goodrich Research and Development Center, Brecksville, OH
44141, U.S.A.
DIANA METODIEWA (Volume III)
Department of Chemistry, University of Alberta, Edmonton, Alberta,
Canada T6G 2G2
ETSUO NIKI (Volume III)
Department of Reaction Chemistry, The University of Tokyo, Hongo,
Bunkyo-ku, Tokyo 113, Japan
XI
Z. OSAWA (Volume II)
Faculty of Engineering, Gunma University, Kiryu, Gunma 376, Japan
D.G. POBEDIMSKIJ (Volume III)
The Kazan Institute of Chemical Technology, Karl Marx-str. 68, Kazan
420015, U.S.S.R.
GREGORY A. REED (Volume III)
Department of Pharmacology, Toxicology, and Therapeutics,
University of Kansas Medical Center, Kansas City, KS 66103, U.S.A.
C.K. RHEE (Volume II)
The Uniroyal Goodrich Tire Company, Brecksville, OH 44141, U.S.A.
TADEUSZ SARNA (Volume III)
Department of Biophysics, Institute of Molecular Biology, Jagiellonian
University, A. Mickiewicza 3, 21-120 Krakow, Poland
GERALD SCOTT (Volumes I, II and III)
Department of Chemical Engineering and Applied Chemistry, Aston
University, Aston Triangle, Birmingham B4 7ET, U.K.
HAROLD M. SWARTZ (Volume III)
University of Illinois, College of Medicine at Urbana-Champaign, 506
South Mathews, Urbana, IL 61801, U.S.A.
PAUL J. THORNALLEY (Volume III)
Department of Chemistry and Biological Chemistry, University of
Essex, Wivenhoe Park, Colchester C04 3SQ, Essex, U.K.
PETER WARDMAN (Volume III)
Cancer Research Campaign, Gray Laboratory, P.O. Box 100, Mount
Vernon Hospital, Northwood, Middlesex HA6 2JR, U.K.
1
Chapter 1
AUTOXIDATION AND ANTIOXID ANTS:
HISTORICAL PERSPECTIVE
GERALD SCOTT
1. THE AGEING OF RUBBER
The phenomena associated with oxidation were recognised long before the
mechanism of autoxidation was developed. Many materials used by man
were known to undergo slow deterioration in the atmosphere. The earliest
investigations of oxidation were carried out on the first technologically
important polymer, natural rubber. Hoffman [1] has been credited with the
discovery that "perishing" of rubber involves the absorption of oxygen. In
retrospect, natural rubber and particularly vulcanised natural rubber, is the
most difficult medium that could be envisaged for the fundamental study of
chemical reactions. Not only is it chemically "impure" when first prepared,
but from the moment at which the latex leaves the tree, oxidation reactions
of both the hydrocarbon and non-hydrocarbon constituents are initiated.
Vulcanisation with sulphur increases the complexity of the system and it
ceases to behave like a simple hydrocarbon. More recent research has shown
that the sulphur cross-link behaves initially as an accelerator of oxidation
(pro-oxidant) but that oxidation products of the sulphides in the cross-link
retard the oxidation process [2]. The oxidation chemistry of sulphur com
pounds will be discussed in later chapters but it should be noted that the
complex behaviour of vulcanised rubber almost certainly accounts for the
phenomenological approach subsequently adopted by scientists and technol
ogists in studying its deterioration under practical conditions. The techno
logical and even the scientific literature contain many anthropomorphic
terms such as "ageing", "fatigue", "perishing" and "poisoning" to describe the
loss of useful properties of rubbers caused by oxidation. These terms reflect
the attempts of early rubber technologists to understand technological
changes by biological analogy. They believed that rubber was in some way
"alive" as it left the rubber tree. It is interesting that biological ageing is
increasingly being seen [3] to involve the same chemical processes that
attracted the attention of early rubber scientists. Somewhat ironically, the
study of the oxidation of the polyunsaturated fatty esters (lipids), which is
2 GERALD SCOTT
believed to be the reason for biological ageing, was pioneered by technolo­
gists with practical interests in the deterioration of foodstuffs and in the
"drying" of polyunsaturated fatty esters used in paint technology [4].
A characteristic of both processes is the existence of an "induction period"
before changes in the properties of the materials can be detected. The reason
for this was recognised at the beginning of the present century when Genthe
[5] was able to show that the characteristic autoaccelerating oxygen absorp­
tion curve [6] was associated with the initial absence and subsequent build
up of hydroperoxides in linseed oil. The addition of partially oxidised turpen­
tine confirmed the conclusion that peroxides are the main initiators for
oxidation. The addition of other peroxides was also found to reduce or
eliminate the induction period. The discovery of peroxides as auto-initiators
for oxidation by molecular oxygen was later found to apply to other sub­
strates, including rubber [6]. It proved to be a key to the development of
antioxidation and antioxidant theory since it applies across the whole
spectrum of autoxidation phenomena. Since peroxides were first recognised
as being important as initiators of oxidation, they have never been far from
the centre of the autoxidation mechanisms.
2. HYDROPEROXIDES AND THE AUTOXIDATION CHAIN REACTION
The chemical structure of peroxides remained rather obscure for many
years. Since unsaturation was found to disappear when olefins were oxi­
dised, it was generally assumed that addition of oxygen to the double bond
was involved and Staudinger [8] gave the name "moloxide" to the four-mem-
bered ring structure, I, believed to be formed,
(a) | |
Iv2C= CR2 * R2C—CR2 (1)
I
An analogous structure (II) was assigned to cyclohexene peroxide by
Stephens [9] but the elegant studies by Criegee [10] and Farmer [11] and
their co-workers, showed that the chemistry of cyclohexene peroxide is
inconsistent with the structure II but can be accounted for by the hydro-
peroxide structure, III.
H «k /OOH
r^S—O
k>a
H
II III
AUTOXIDATION AND ANTIOXIDANTS: HISTORICAL PERSPECTIVE 3
The elucidation of the structure of cyclohexene and related peroxides
formed by the reaction of oxygen with hydrocarbons prepared the way for
the general theory of hydrocarbon autoxidation [12]. Bäckström had applied
Bodenstein's chain reaction theory to the autoxidation of aldehydes in the
presence of light [13]. Unlike earlier workers who discussed chain reactions
in terms of energetic intermediates, Bäckström recognised the free radical
nature of the peroxyl radical intermediate and formulated clearly for the
first time the now well-known radical chain process: Reactions (2) and (3).
RC=0 > RCOO (2)
O O
II II
RCOO+RCHO > RCOOH + RC=0 (3)
In the hands of Bolland, Bateman and Gee and their co-workers [14-23],
at the British Rubber Producers Association, this theory provided a basis for
understanding the role of the hydroperoxide in the auto-initiation Reaction
(4),
Δ,Λν
ROOH » RO+OH- (4)
and by analysis of the kinetics of olefin oxidation they were able to show that
the rate constant of Reaction (5) is normally very much faster than that of
Reaction (6).
00·
I
R'CH = CH-CH- + 0 > R'CH=CHCH-
2
(RO (ROO) (5)
ROO· + R'CH = CHCH - > ROOH + R'CH= CHCH- (6)
2
and hence the overall rate at normal oxygen pressures is to a large extent
dependent on the rate constant of Reaction (6).
The full implications of the Bolland, Bateman, Gee mechanism will be
discussed in Chapter 2 of this volume but some of them have great signifi­
cance for the subsequent development of antioxidant theory and will be
briefly noted here:
(a) Termination at atmospheric oxygen pressures is normally by bi-
molecular reaction of two alkylperoxyl radicals. Russell showed [24-26] that
when the peroxyl radical contains an α-hydrogen, this is predominantly by
disproportionation:
4 GERALDSCOTT
R
\ P~°
2RR'CHOO'->C O' > RCOR' + RR'CHOH + O, 07)
R HO
R I
RCHR'
However, at low oxygen pressures or when the intermediate alkyl radical is
stabilised by resonance, then termination Reactions (8) and (9) involving
alkyl may also occur [21,23].
ROO+R· » ROOR (8)
2R· ► R-R (9)
(b) Although propagation occurs in saturated molecules and in many
olefins by Reaction (5), if there is no reactive methylene group in an olefin,
as in the case of styrene, then Reaction (5) cannot occur and copolymeriza-
tion results to give a polyperoxide by Reaction (6) [27], as proposed earlier
by Milas [28].
PhCH=CH + ROO ► PhCH-CHOOR
2 2
(10)
PhCHOO
I
ROO[CH CHOO] -CH CH-00· *— CH OOR
2 n 2 2
I
Ph Ph n PPhhCCHH =CH
2
+ n0
2
3. ANTIOXIDANTS
As we have seen, rubber technology was well advanced before the theory
of autoxidation was developed and the early discovery of protective agents
for rubber was entirely empirical. Thus a patent for the use of phenol and
p-cresol appeared in 1870 [29] and for hydroquinone and pyrogallol in 1901
[30]. An important discovery was that some chemicals (e.g. aniline) used in
the "curing" or "vulcanisation" of rubber could have a profound retarding
effect on subsequent ageing [31]. It was later shown that sulphur-containing
accelerators for vulcanisation (e.g. mercaptobenzthiozole and the thiuram