Hydroxy sulfur compounds

Other general procedures for carbonyl alkylidenation are based upon the following P-hydroxy sulfur compounds ... 

Diisobutylaluminum phenyl selenide, 117 Triphenyltin hydride, 335 Hydroxy sulfur compounds Diisobutylaluminum hydride, 115 Methylthiomethyllithium, 192 Thiophenol, 53, 312... 

The term naphthenic acid, as commonly used in the petroleum industry, refers collectively to all of the carboxyUc acids present in cmde oil. Naphthenic acids [1338-24-5] are classified as monobasic carboxyUc acids of the general formula RCOOH, where R represents the naphthene moiety consisting of cyclopentane and cyclohexane derivatives. Naphthenic acids are composed predorninandy of aLkyl-substituted cycloaUphatic carboxyUc acids, with smaller amounts of acycHc aUphatic (paraffinic or fatty) acids. Aromatic, olefinic, hydroxy, and dibasic acids are considered to be minor components. Commercial naphthenic acids also contain varying amounts of unsaponifiable hydrocarbons, phenoHc compounds, sulfur compounds, and water. The complex mixture of acids is derived from straight-mn distillates of petroleum, mosdy from kerosene and diesel fractions (see Petroleum). 

The tautomerism of 2-substituted 1,3-azoles (154 155) is summarized in Table 39. Whereas amino compounds occur Invariably as such, all the potential hydroxy derivatives exist in the 0x0 form, and in this series the sulfur compounds resemble their oxygen analogs. There is a close analogy between the tautomerism for all these derivatives with the corresponding 2-substltuted pyrldines. 

The second Mycobacterium strain capable of DBT desulfurization was M. phlei WU-F1 [30], This strain was also reported to desulfurize naphtho[2,l-b]thiophene (NTH) and 2-ethyl-NTH to sulfur free products with the following intermediates for the latter molecule 2-ethyl-NTH sulfoxide, l-(2 -hydroxynaphthyl)-l-butene, and l-naphthyl-2-hydroxy-1-butene [94], Thus, this organism was reported to consist of a sulfur-specific pathway capable of desulfurization of broad range of sulfur compounds including symmetric and asymmetric molecules. 

Free amino acids are further catabolized into several volatile flavor compounds. However, the pathways involved are not fully known. A detailed summary of the various studies on the role of the catabolism of amino acids in cheese flavor development was published by Curtin and McSweeney (2004). Two major pathways have been suggested (1) aminotransferase or lyase activity and (2) deamination or decarboxylation. Aminotransferase activity results in the formation of a-ketoacids and glutamic acid. The a-ketoacids are further degraded to flavor compounds such as hydroxy acids, aldehydes, and carboxylic acids. a-Ketoacids from methionine, branched-chain amino acids (leucine, isoleucine, and valine), or aromatic amino acids (phenylalanine, tyrosine, and tryptophan) serve as the precursors to volatile flavor compounds (Yvon and Rijnen, 2001). Volatile sulfur compounds are primarily formed from methionine. Methanethiol, which at low concentrations, contributes to the characteristic flavor of Cheddar cheese, is formed from the catabolism of methionine (Curtin and McSweeney, 2004 Weimer et al., 1999). Furthermore, bacterial lyases also metabolize methionine to a-ketobutyrate, methanethiol, and ammonia (Tanaka et al., 1985). On catabolism by aminotransferase, aromatic amino acids yield volatile flavor compounds such as benzalde-hyde, phenylacetate, phenylethanol, phenyllactate, etc. Deamination reactions also result in a-ketoacids and ammonia, which add to the flavor of... 

Peroxide Decomposers. Aryl phosphites and certain sulfur compounds such as sulfides, disulfides, and thiodipropionate esters decompose peroxides into inactive compounds which do not promote polypropylene oxidation. These chemicals function by extracting an oxygen atom from the peroxide group and reducing it to an ether or hydroxy group (9). 

It has long been known that a thiol and an alkene react in an atmosphere of oxygen at room temperature to give /i-hydroxy sulfoxides64, compounds with stereogenic centers at the ft-carbon and the sulfinyl sulfur. 

The efficient decomposition of hydroperoxides by a non-radical pathway can greatly increase the stabilizing efficiency of a chain-breaking antioxidant. This generally occurs by an ionic reaction mechanism. Typical additives are sulfur compounds and phosphite esters. These are able to compete with the decomposition reactions (either unimolecular or bimolecular) that produce the reactive alkoxy, hydroxy and peroxy radicals and reduce the peroxide to the alcohol. This is shown in the first reaction in Scheme 1.69 for the behaviour of a triaryl phosphite, P(OAr)3 in reducing ROOH to ROH while itself being oxidized to the phosphate. 

Sulfur tetrafluoride was among the first reagents to be used for the direct substitution of hydroxy groups by fluorine. Good yields are only achieved with relatively acidic alcohols, such as nitro alcohols, polyhalo alcohols and hydroxy carbonyl compounds. The fluorination of simple aliphatic alcohols with sulfur tetrafluoride results in side reactions, such as formation of ethers, hence fluorination using other methods (vide infra) is preferred. Moreover, sulfur tetrafluoride cannot be handled without special pressure apparatus and requires precautions to be taken due to its physical and toxicological properties, hence it is, nowadays, frequently replaced by other reagents, but it is still in use for relatively inert substrates (see Vol.ElOa, p 321 ff, also Houben-Weyl. Vol. 5/3. pp 84-86). 

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