Phenols from sulphides

A range of polysulphones has been prepared with a variety of bis-phenols other than bis-phenol A. As might be expected from the discussion in Chapter 4 and from experience with the range of polycarbonates (Chapter 20), replacement of the isopropylidene link with a methylene, sulphide or oxygen link depresses the Tg whilst —C(CgH5)2— and sulphone links raise it. The bis-phenol derived from norcamphor leads to a polysulphone with a Tg of 250°C (195°C for a Udel-type polymer). 

With a somewhat lower level of heat resistance but with many properties that make them of interest as engineering materials alongside the polycarbonates, polysulphones, poly(phenylene sulphides) and polyketones are the so-called polyarylates which are defined as polyester from bis-phenols and dicarboxylic acids. 

Synergism can also arise from cooperative effects between mechanistically different classes of antioxidants, e.g., the chain breaking antioxidants and peroxide decomposers (heterosynergism) [42]. For example, the synergism between hindered phenols (CB—D) and phosphites or sulphides (PD) is particularly important in thermal oxidation (Table 2). Similarly, effective synergism is achieved between metal dithiolates (PD) and UV-ab-sorbers (e.g., UV 531), as well as between HALS and UV-absorbers, (Table 3). 

Loss of catalytic activity resulting from internal displacements is not usually a serious problem below temperatures of about 100 C. However, highly active R-groups, such as benzyl, methyl and allyl, undergo internal displacement more readily, particularly in the presence of strong nucleopfiles. For instance, the presence phenolates and thiolates may lead to the formation of benzyl alcohol, ethers, or sulphides from benzyl-substituted quaternary ammonium salts. 

Alkylphenols are weak acids, but substitution on the alkylphenol with methylene or sulphur increases the acidity. The methylene-substituted phenates originate from a condensation product between the alkylphenol and formaldehyde. Phen-ate sulphides can be obtained by at least three sulphurization reagents (1) sulphur monochloride, (2) sulphur dichloride and (3) elemental sulphur. The percentage of sulphur contained in a phenate sulphide detergent directly dictates the chemistry of the detergent because of the variable ratio of sulphur atoms to alkylphenol substrate and the variety of ways the sulphur atoms can be attached to the alkylphenol. Phenol detergents are more difficult materials to describe based on analytical data. Nevertheless, the same chemical concepts applied to sulphonates also apply to phenates. Table 7.2 summarizes the compositional ranges typically observed in phenate lubricant additives. 

In the case of industrial wastewater, several other compounds can also be involved, such as sulphide, hexavalent chromium or organic molecules. This last group of compounds is considered hereafter with regard to their economic and/or environmental importance. For example, Fig. 5 presents several specific compounds encountered in refinery and petrochemical wastewater. Thus, phenol, EPA (ethylpropylacrolein), TBC (tertiobutylcatechol), NMP (/V-methylpyrolidone) and nitrite can be detected in effluents or process water [21], Moreover, the estimation of complementary aggregate parameters, such as total oxygen demand (TOD), is possible from the estimation of one of the previous organic compounds [3] (Fig. 6). 

Sulphur interrupts the conjugation between phenolic nuclei. Therefore, unpaired electron is delocalized mostly over one phenolic nucleus in phenoxyls formed from 2,2 -thiobisphenols CLXVII23). Only about 15% of the density of unpaired electrons is delocalized to the sulphur of the sulphidic bridge. As a consequence, the stability... 

The above facts indicate a facile formation of phenoxyls from phenolic sulphides during the inhibition process as well as stabilization of phenoxyls due to the presence of sulphur atom in bridge even when sulphur is separated from the aromatic nucleus by a methylene group. 

Resonance effect connected with the formation of cyclohexadienonyl radical and its subsequent transformation into alkylperoxycyclohexadienone were proved in phenoxyls derived from monohydric phenols (Chap. II C.l). The possibility of participation of such reactions in transformations of phenolic sulphides of types CLXVII and CLXVTII can be assumed from data obtained in the oxidation by excessive alkylperoxyls22, 23l The recombination of alkylperoxyls occurs and active... 

The radicals CXC were formed from CXCVIIa also by oxidation with oxygen bonded to Co(II)acetylacetonate22. This results from the electron density distribution in dibenzyl sulphide CXCVIIa, which behaves as an alkylsubstituted mononuclear phenol. 

An induction period was observed in the decomposition of cumyl hydroperoxide in chlorobenzene at 70 and 110 °C in the presence of phenolic sulphides CXCVIIa,b262). This was a substantial difference with respect to the behaviour of 4,4 -thio-bis(2,6-di-tert-butylphenol) CLXVIIIb which decomposed ROOH under the same conditions without induction period. The result indicates a mechanistic distinction in the action of both types of phenolic sulphides. In the mechanism of transformations of benzyl sulphide CXCVIIb, there are assumed (Scheme 24) the formation of sulphoxide CXCVIII and the intermediary formation of CIC followed by oxidation and formation of sulphinic acid CC. Further transformation of the acid CC depends on the character of R. If R = 3,5-di-tert-butyl-4-hydroxybenzyl, as it is in the formation of CC from CXCVIIa, the total elimination of the sulphurous part of molecule may occur and the transformation products of phenolic or quinoid character may be formed 3,5-di-tert-butyl-4-hydroxybenzyl alcohol XXXI, the corresponding aldehyde XXXII, and 2,6-di-tert-butyl-l,4-benzoquinone XXII were identified. Another possible sulphurless product is 4,4 -ethylenebis(2,6-di-tert-butyl-phenol) XXVIII, which was isolated in small amounts in its oxidized form as 3,5,3 ,5 -tetra-tert-butyl-4,4 -stilbenequinone (XXIX). Quinone methide XXX formed by thermolysis of sulphoxide CXCVIII, may be also the precursor in formation of XXIX. According to66), XXX is further oxidized by hydroperoxides to XXIX... 

It was shown with two types of phenolic sulphides that both reaction centres take part in transformation processes which proceed under the conditions of inhibited oxidation of polymers. The phenolic part of the molecule participates in the inhibition mechanism by processes which follow from its chain-breaking function. Not only the starting phenolic sulphides react in this way, but also the phenolic compounds which were formed by reactions at the second centre, i. e., at sulphidie sulphur, and the products of their consecutive transformations. Transformations of the sulphidie part of the molecule are connected with preventive mechanism of antioxidation action, which is characterized by the decomposition of hydroperoxides. 

From the viewpoint of chemical and physical requirements the permissible indicators involve a number of criteria mercury, selenium, cadmium, vanadium, chromium, arsenic, silver, lead, barium, cyanides, hydrogen sulphide, fluorides, phenols, oil and oil substances, COD(Mn), colour, odour, taste and turbidity. The most stringent criterion concerns the content of mercury, followed by selenium, cadmium, vanadium, cyanides, oil and oil substances. Another important indicator is the content of organic matters characterized by COD(Mn). 

---