Sulfur compounds formed from antioxidants

Sulfur compounds in crude oil sharply decreases the quality of fuels and oils produced from the crude oil. They cause corrosion of equipment during treatment, reduce activity of antidetonation additives and antioxidizing stability of gasoline, raise the propensity to form hard residues in cracking gasoline fractions, and result an environment pollution. 

Materials that are not eflfective inhibitors when used alone may nevertheless be able to function as synergists by reacting with an oxidized form of an antioxidant to regenerate it and thus prolong its effectiveness. For example, carbon black forms an effective combination with thiols, disulfides, and elemental sulfur, even though these substances may be almost completely ineffective alone under comparable conditions. Synergistic combinations from a variety of chain terminators and sulfur compounds have been reported. A widely used combination of stabilizers for polyolefins is 2,6-di-ferf-butyl-4-methylphenol (BHT) (Figure 1.41a) with dilauryl thiodipropionate (DLTDP) ... 

The primary aromatic substances in beer are derived from raw materials (barley or hops) that confer the beer s typical odour and taste. Bitter acids of hops have a bitter taste (see Section 8.3.5.1.3), but hop cones also contain 0.3-1% m/m of terpenoids (60-80% of hop essential oil), which have a considerable influence on the smell of beer. The main components of aromatic hop oils are sesquiterpenic hydrocarbons in which a-humulene, P-caryophyllene and famesene dominate. The major monoter-penic hydrocarbon is myrcene. For example, the essential oil content of fine aromatic varieties, such as Saaz, is 0.8% m/m, of which 23% is myrcene, 20.5% a-humulene, 14% famesene 6% and P-caryophyUene. Significant components of the hop aroma in beer are mainly isomeric terpenoid monoepoxides resulting from autoxidation and diepoxides of a-humulene and fS-caryophyUene, but also other terpenoids. Important components of hops odour are also various alcohols (such as geraniol and hnalool), esters (ethyl 2-methylpropanoate, methyl 2-methylbutanoate, propyl 2-methylbutanoate and esters of terpenic alcohols, such as geranyl isobutanoate), hydrocarbons, aldehydes and ketones formed by oxidation of fatty acids, such as (3E,5Z)-undeca-l,3,5-triene, (Z)-hex-3-enal, nonanal, (Z)-octa-l,5-dien-3-one, their epoxides, such as ( )-4,5-epoxydec-2-enal and sulfur compounds. Other important components of hops are so-called polyphenols (condensed tannins) that influence the beer s taste and have antioxidant effects. Less important compounds are waxes and other hpids. Hop products, such as powder, pellets and extracts (by extraction with carbon... 

The function of an antioxidant is to divert the peroxy radicals and thus prevent a chain process. Other antioxidants function by reacting with potential initiators, and thus retard oxidative degradation by preventing initiation of chains. Many sulfur and phosphorus compounds are believed to function in the latter way. The hydroperoxide products from autoxidation are potential chain initiators. This fact gives autoxidations the potential of being autocatalytic, since the more oxidation product is formed, the higher the initiator concentration. Divalent sulfur compounds and trivalent phosphorus compounds can reduce hydroperoxides, yielding stable products ... 

As mentioned above, many stabilizers are deactivated to other products during their first service for example, phenolic antioxidants to quinonemethides, cyclohexadienones or benzoquinones phosphates are formed from phosphites various oxidation products of sulphides, including organic acids of sulfur, from sul-phidic heat stabilizers and substituted piridin-4-one and open-chain nitroso and nitro compounds, salts and other transformation products arising from HAS. Stabilizers are also lost by diffusion and migration. 

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