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AZ9RBAYCAN KIMYA JURNALI № 4 2017
89
UDC 554;544.4;544.344
MECHANISM OF MUTUAL INFLUENCE AND INTERCONNECTION OF ANTIOXIDATIVE ACTION OF PHENOL-, AMINO- AND SULPHUR-GROUPS
A.M.Kashkay, O.T.Kasaikina*, N.M.Hasanguliyeva
M.Nagiev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan *Institute Chemical Physics, Russian Academy of Sciences
kashkay@mail.ru Received 25.01.2017
A study is made of the influence of polyphenolsulfides on decomposion of hydroperoxide of cumin. An effect of increasing the time of expenditure of hydroperoxide in diluted solutions relatively the concentrated ones has been determined; this indicator is a consequence of autocatalytic process. There has been established a phenomenon of deactivation of polyphenol sulfides as catalysts of desintegration of the reaction with peroxiradicals. The kinetic characteristics of interaction of the given substances.
Keywords: polyphenol sulfide, hydroperoxide of cumin, auto catalytic process, hydrogenated quinoline.
Introduction
The effective stabilization of organic materials by utilizing micro-additives of non-toxic antioxidants has acquired recently an ecological importance in parallel with a well-known economic benefit. An increase of the material life in-service is counterpart to the increase of their production without ecological overhead of the chemical industry. Various kinds of synthetic phenols, aromatic amines and some other compounds interacting efficiently with peroxyl radicals have been used as antioxidants [1-3]. In the protection of sensitive unsaturated hydrocarbon systems 6-ethoxy-2,2,4-trimethyl-l,2-dihydroquinoline (ethoxyquin, HQi) process a remarkable antioxidant activity. They are also added to fodder. Antimutagenic effects, and allergenic activities of the product have also been studied.
In recent years new results have been obtained for polyfunctional antioxidants, which exhibit excellent antioxidant activity combining in their molecules phenol, amine, metal and sulphur containing fragments. This paper deals with characteristics of antioxidant activities of polyfunctional antioxidants namely polyphenol-and aminophenolsulphides (PPSi-PPS6) as well heterocyclic amines (hydrogenated quinolines) that include phenol and sulphur-containing groups in molecules (HQ1-HQ4). Special attention has been given to the interplay of
inhibiting groups and its effect on the reactivity and transformations in the course of oxidation.
Experimental part
Materials and methods. Polyphenolsul-phides (PPS1-PPS6, see below) were synthesized at the Institute of Supplement Chemistry (Azerbaijan, Baku). Hydrogenated quinolines (HQ1-HQ3) were synthesized at the Institute of Chemical Physics (Moscow) and HQ4 - at the Voronezh State University (Russia). The purity of the compounds was monitored:
OH
OH
OH
-S-S
C(CH3)3
-S-S —
C(CH3)3
OH
OH
-S-CH,-S-
C(CH3)3
OH
- S-CH2-S —
C(CH3)3
C(CH3),
OH
OH
Ol ^-for^l o
C(CH3)3
C(CH3)3
PPS,
C(CH3)3
C(CH3)3
OH
OH
-S-CH,
C(CH3)3
PPS
C(CH3)3
OH
C(CH3)3
SH
- S-CH2-CH-CH2-NH
PPS,
o
C,H5O.
N
I
H
HQi
HQ,
The initiated with AIBN oxidation reactions of cumene and ethylbenzene at 60V were used as model reactions for determination of ki - the rate constant for the interaction of antioxidant (InH) with peroxyl radicals (RO2); / - stoichiometric inhibition coefficient that shows the number of chain termination steps per one molecule InH [4]. These kinetic parameters were determined according to [5, 9]. The rate of oxygen consumption was measured in a reaction vessel connected to a gas-meter unit under O2 pressure of 760 Torr.
The relative efficiency of different an-tioxidants has been estimated by induction period values t, determined under the same conditions. We have compared the PPS efficiency in the cumene autooxidation at 1100C. The autooxidation of B-carotene at 500C in n-xylene solution, the autooxidation of isoparaf-finic oil at 1500C and n-decane at 1500C were used as model reactions for testing of HQ derivatives. The hydrocarbons (RH) were oxidized in thermostated bubbling-type vessels in a
SH
I
S-CH2-CH-CH2-NH
C(CH3)3
o
C(CH3)3
PPS6
N
I
H
HQ3
H HQ4
stream of oxygen (1.61 h-1). The oxidation rate was monitored by the accumulation of hydroperoxides (HPC) (cumene, isoparaffinic oil, n-decane), whose content was measured by iodometric method. The decomposition of cumene hydroperoxide (HPC) was conducted in an ultrahigh-purity nitrogen flow (1.6 1/ h).
The concentration of B-carotene was followed spectroscopically.
B-Carotene was purchased from HoffmanLaRoche Co. Cumene, n-decane were purified according to standard procedures, and isoparaffinic oil was used without further purification.
Results and discussion
Table shows the values of effective rate constants and stoichiometric inhibition coefficients for PPS,, and HQ,. There should be noted two important moments: (1) k for PPS are much less than that for HQ and BHT, the induction periods in the cumene autooxidation in the presence of PPS are longer than that in the presence of ethoxyquin (HQ1) and BHT;
O
H
Kinetic characteristics of antioxidant activity for polyphenolsulphides and hydrogenated quinolines
Inhibitor ak,(1/s) af T(h) d -10 5(hdm3mol 1 ) xrel V '
PPS1 2.4-103 «10 "11.3 "(22.5) —
PPS2 2.4-103 10 "8.2 -
PPS3 6.6-103 10 "12.5 -
PPS4 3.2-103 6 b7.5 -
PPS5 2.4-103 4 "6.1 -
PPS6 2.5-103 4 "8.1 -
HQ1 1.3-106 1.3 "0.5 c0.6 3.1
HQ2 2.6-106 2 c11.6 7.5
HQ3 7.4-106 1.9-1.4 c4.5 4.0
HQ4 1.5-103 1.6 c3.8 c1.5 0.7
BHT 2.5104 2 c2.1 0.8
"Initiated by AIBN oxidation of cumene (for PPS) and ethylbenzene (for HQ) at 600C. ^Induction periods determined in cumene autooxidation at 1100C, concentration of PPSs 2.5-10-6mol/dm3 "Induction periods determined in isoparaffinic oil autooxidation at 1500C, InH concentration 110-4 mol/dm3. ^Induction periods determined in 5 mmol/dm3 B-carotene autooxidation at 500C, Trel= t /[InH].
(2) hydroxy substituted HQ2 and HQ3 have demonstrated high kt. They exhibit the most retardation both in isoparaffin oil at high temperature and in B-carotene oxidation at moderate temperature as opposed to HQ1 being none-effective at high temperature and HQ4 - relatively less active at moderate temperature. Some reasons of the contradiction mentioned are discussed below in connection with the inhibitors structures and the interplay of different inhibiting groups.
PPS1-PPS6 have been found to be effective catalysts for the cumene hydroperoxide (HPC) decay (Figure 1). HPC decomposition in the presence of PPS occurs as an autocatalytic process that consists of some stages. A new effective catalyst (Pi) is formed from the initial PPSi in the course of HPC decomposition. The maximum rate of HPC decay Wmax follows the equation [10]:
Wmax = k* [HPC]o[PFSi].
In the case of PPS1-3 the effective rate constants for the catalytic HPC decay k* are 45-fold higher than k* for bisphenol PPS4 and more than 100-fold higher of k* for monophe-nolsulphides. One of the possible trivial causes
for such a difference may be the different yield of catalysts Pi derived from PPS,: when a catalyst is produced via an oxidative transformation of PPSi the more of the same type fragments is contained, the more catalyst it produced.
Time, min
Fig. 1. Kinetic curves of cumene hydroperoxide decomposition in the presence of 0.1 mmol /dm3 PPS2 at 1100C in chlorobenzene solution (under nitrogen).
The HPC decay catalyzed by PPSi undergoes with a low free radical formation; the yield of free radicals in the case of HPQ and PPS3 has been found to be less than 3-l0-4 [11, 12]. The PPSi transformation products formed in the reaction with HPC, exhibit antioxidant properties to a greater extent than the initial PPS,- species. Table shows that the induction period in cumene
autooxidation in the presence of PPS1 (11.3 h) is less than t=22.5 h obtained in the presence of the same amount of PPS1 that had previously degraded 50 mmol/dm3 HPC (under N2 atmosphere). Probably these properties of PPSi are responsible for the high stoichiometric inhibition coefficients and long-term induction periods in cumene oxidation in the presence of PPS^
The HQ4 molecule contains three sulphur atoms being combined in dithiolthione ring fused to heterocycle of HQ4, including the NH group. Small additive of HQ4 (0.1 mmol/dm3) accelerates the HPC (10 mmol/dm ) decay. However, the catalytic activity of HQ4 is relatively low: the number of catalytic cycles and the effective rate constant for the HPC decay in the presence of HQ4 has been found to be 100-fold lower than k* for PPS^ When the same small amount of HQ4 is added to «-decylhydroperoxide (at 1200C)
a stoichiometric reaction occurs which does not practically change the rate of hydroperoxide thermal decay [12]. It means that the hydroperoxide nature is of great importance for its interaction with a sulphur-containing antioxidant. The HPC decay is known to result in phenol formation when it proceeds in the presence of sulphur-containing antioxidants and acids [13]. A synergism between sulphur compounds and phenol in the retardation of hydrocarbon oxidation has been noted. We have suggested that phenol is a necessary component of the reaction mixture for catalytic hydroperoxide decay in the presence of sulphur compounds; together with a hydroperoxide they form acid-like catalysts that result in mostly heterolytichydroperoxide decay. In spite of PPS, HQ4 does not contain phenolic groups, so the catalysis of the HPC decay in the presence of HQ4 is likely due to formation of phenol, derived from HPC [14-16].
The fused dithiolthione ring has been shown to act as an electron-accepting substituent that makes itself evident in the decrease of ki (compare HQ1 and HQ4, Table).
Table shows that hydrogenated quinolines HQ1 and hydroxy substituted HQ2 and HQ3 are highly reactive in the chain-breaking step:ki for these HQ are 10-fold and more higher than ki for the most of common chain-breaking antioxidants
of phenol and amine types [16]. These compounds demonstrate the most long-term induction periods in B-carotene oxidation. However, at elevated temperatures (>1000C) HQ1 lost antioxidant properties (Table and Figure 2) whereas HQ2 and HQ3 are effective antioxi-dants in a wide temperature range. The study of nature and reactivity of intermediate radicals, derived from HQ, has clarified the cause of these differences.
200
400 Time, min
1000
Fig. 2. Kinetic curves of n-decane hydroperoxide accumulation in the course of autooxidation in the presence of 0.2 mmol/dm3 HQ, at 150°C: 1 - without additives, 2 - HQ1,
3 - HQ4, 4 - HQ3, 5 - HQ2.
The first stage of the mechanism of antioxidant action of ethoxyquin (HQ1) consists in transfer of the amine hydrogen atom to alkyl peroxy radicals, which is accompanied by the formation of alkylhydroperoxide and of aminyl-radical. This breaks the kinetic autooxidation chains. The aminyl-radical resulting from HQ1 decays at elevated temperatures (>1000C) to form an active methyl radical and 2,4-dimethyl-quinoline:
C2H5O
C2H5O
+ CH3.
N'
N'
CH3 participates in the chain propagation, so HQ1 and the hydrocarbon are oxidized together. Hydroxysubstituted HQ2 and HQ3 having both -OH and -NH groups in the molecule can
react with R0'2 to form accordingly phenoxyl-
(PhO) or aminyl-radicals. The investigation of free radical and molecular transformation products of HQ2 and HQ3 has shown that the initial attack of RO2 is directed mainly toward hydroxyl group. According to the X-ray data in HQ2 the neighbouring -OH and -NH groups are bonded by an intramolecular hydrogen bond between the oxygen atom of the hydroxyl and the
hydrogen of the amine group. The interaction of HQ2 with RO2 results in the formation of phenoxyl radical that is persistent under ambient conditions in the presence of oxygen. The hyperfine structure of the phenoxyl suggests the interaction of unpaired electron with nitrogen and four non- equivalent protons. GC-MS analysis has shown that the main transformation product of HQ2 in free radical oxidation is quinone (Q) with unchanged heterocycle:
MNDO and ab initio calculations of HQ2 molecule and the corresponding phenoxyl and aminyl radicals have pointed to the favoured phenoxyl formation resulting from the H-atom abstraction from OH-group of HQ2.
6-Hydroxysubstituted HQ3 is an active R0'2 acceptor as well (Table). The corresponding quinone-imine (Q1) has been found to be the main HQ3 transformation product in free radical oxidation:
The peroxyl-radical scavenging action of HQ3 has been ascribed to the initial reaction of the phenol hydrogen resulting in a short-lived phenoxyl radical.
The /NH group in fused heterocycle acts as a strong electron donor substituent similarly to the chroman cycle in a-tocopherol which is one of the most important antioxidants in vivo and has ki of the same order of magnitude as HQ2 and HQ3.
Summarizing the data on the antioxidant activity of the inhibitors above one can conclude that the mechanism of mutual influence and interrelated antioxidant action of amino-, phenol-and sulphur-groups, being connected in the poly-
functional antioxidants, has several levels. In the intramolecular level the groups act on the base of general laws for the electron transfer effect resulting in the change of the individual fragment reactivity: OH-, NH-, RS- are electron donor substituents, dithiolthione cycle - an electron accepting group. A marked cooperative antioxidant effect of sulphur-containing inhibitors is realized in the intermolecular level and obviously needs phenols and hydroperoxides for its realization. The basis for cooperative effect is the formation under participation of phenols, sulphur groups, and hydroperoxides, some active components, which catalyze hydroperoxide decay and take part in the chain breaking.
References
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AMÍN-, FENOL-, SULFO-QRUPLARIN ANTÍOKSÍDLO§DÍRlCÍ TOSÍRLORINÍN QARSILIQLI TOSÍR VO aLAQOLORlNiN MEXANÍZMÍ
A.M.Qaçqay, O.T.Kasaikina, N.M.Hasanquliyeva
Hidroperoksid kumilin parcalanmasina polifenolsulfidin (PFS) tasiri ôynnilmiçdir. Hidroperoksidin qati mahlulla müqayisada duru mahlulda sarf olunmasi vaxtinin effektivliyi müayyan olunmuçdur. Hansi ki, bu avtokatalitik proses naticasinda ózünü gôstarir. Polifenolsulfidin peroksiradikalla reaksiyada va kumilhidroperoksidin parçalanmasinda yaranan katalizatorun aktivliyini açagi saldigi mûçahida olunmuçdur. istifada olunan maddalarin qarçiliqli tasirinin kinetik xüsusiyyatlari müiyyan olunmuçdur.
Acar sozlar: polifenolsulfid, kumil hidroperoksid, avtokatalitik proses, hidrogenh§mi§ xinolinmhr.
МЕХАНИЗМ ВЗАИМНОГО ВЛИЯНИЯ И ВЗАИМОСВЯЗИ АНТИОКИСЛИТЕЛЬНОГО ДЕЙСТВИЯ ФЕНОЛ-, АМИНО- И СУЛЬФОГРУПП
А.М.Кашкай, О.Т.Касаикина, Н.М.Гасангулиева
Исследовано влияние полифенолсульфидов на распад гидропероксида кумила. Установлен эффект увеличения времени расходования гидропероксида в разбавленных растворах относительно концентрированных; этот показатель является следствием автокаталитического процесса. Установлено явление дезактивации полифенолсульфидов как катализаторов разложения в реакции с пероксирадикалами. Рассчитаны кинетические характеристики взаимодействия указанных веществ.
Ключевые слова: полифенолсульфид, гидропероксид кумила, автокаталитический процесс, гидрированные хинолины.
AЗЕРБAЙДЖAНСКИЙ ХИЫИЧЕСКИЙ ЖУРНЛЛ № 4 2017
