Sulfates esterification

Sulfate can be converted to the sulfate donor compound 3 -phosphoadenosine-5 -phosphosulfate (PAPS) in a two-step reaction (Figure 17-17). PAPS participates in the sulfate esterification of alcoholic and phenolic functional groups (e.g., in synthesis of sulfolipids and glycosamino-glycans). 

PAPS is an activated sulfate compound and is an intermediate in all organisms for sulfate esterification, such as the synthesis of chondroitin sulfate. 

CS 6-O-sulfate Esterification using inorganic acids Polyampholite soluble in water Anticoagulant Haemagglutination inhibition activities Anti sclerotic Antiviral Antihuman immunodeficiency virus Antibacterial Antioxidant Enzyme inhibition activities... 

J. Rebek, Jr., (1987) first developed a new synthesis of Kemp s acid and then extensively explored its application in model studies. The synthesis involves the straightforward hydrogenation (A. Steitz, 1968), esterification and methylation of inexpensive 1,3,5-benzenetricar-boxylic acid (trimesic acid 30/100 g). The methylation of the trimethyl ester with dimethyl sulfate, mediated by lithium diisopropylamide (V. J. Shiner, 1981), produced mainly the desired aff-cis-1,3,5-trimethyl isomer, which was saponified to give Kemp s acid. 

The sulfuric acid hydrolysis may be performed as a batch or continuous operation. Acrylonitrile is converted to acrylamide sulfate by treatment with a small excess of 85% sulfuric acid at 80—100°C. A hold-time of about 1 h provides complete conversion of the acrylonitrile. The reaction mixture may be hydrolyzed and the aqueous acryhc acid recovered by extraction and purified as described under the propylene oxidation process prior to esterification. Alternatively, after reaction with excess alcohol, a mixture of acryhc ester and alcohol is distilled and excess alcohol is recovered by aqueous extractive distillation. The ester in both cases is purified by distillation. 

A.lkylSulfoacetates. These surfactants are prepared by esterification of sulfoacetic acid or by sulfonation of the alkyl chloroester. They are considered to produce good foaming and are less irritating to the eyes than the alkyl and alkyl ether sulfates (10). 

Although soaps have many physical properties in common with the broader class of surfactants, they also have several distinguishing factors. First, soaps are most often derived direcdy from natural sources of fats and oils (see Fats and fatty oils). Fats and oils are triglycerides, ie, molecules comprised of a glycerol backbone and three ester-linked fatty oils. Other synthetic surfactants may use fats and oils or petrochemicals as initial building blocks, but generally require additional chemical manipulations such as sulfonation, esterification, sulfation, and amidation. 

Zinc chloride is a Lewis acid catalyst that promotes cellulose esterification. However, because of the large quantities required, this type of catalyst would be uneconomical for commercial use. Other compounds such as titanium alkoxides, eg, tetrabutoxytitanium (80), sulfate salts containing cadmium, aluminum, and ammonium ions (81), sulfamic acid, and ammonium sulfate (82) have been reported as catalysts for cellulose acetate production. In general, they require reaction temperatures above 50°C for complete esterification. Relatively small amounts (<0.5%) of sulfuric acid combined with phosphoric acid (83), sulfonic acids, eg, methanesulfonic, or alkyl phosphites (84) have been reported as good acetylation catalysts, especially at reaction temperatures above 90°C. 

There are two main processes for the synthesis of ethyl alcohol from ethylene. The eadiest to be developed (in 1930 by Union Carbide Corp.) was the indirect hydration process, variously called the strong sulfuric acid—ethylene process, the ethyl sulfate process, the esterification—hydrolysis process, or the sulfation—hydrolysis process. This process is stiU in use in Russia. The other synthesis process, designed to eliminate the use of sulfuric acid and which, since the early 1970s, has completely supplanted the old sulfuric acid process in the United States, is the direct hydration process. This process, the catalytic vapor-phase hydration of ethylene, is now practiced by only three U.S. companies Union Carbide Corp. (UCC), Quantum Chemical Corp., and Eastman Chemical Co. (a Division of Eastman Kodak Co.). UCC imports cmde industrial ethanol, CIE, from SADAF (the joint venture of SABIC and Pecten [Shell]) in Saudi Arabia, and refines it to industrial grade. 

Other examples of esterification with trialkyloxonium salts have been reported.7,8 The present procedure offers the advantages that the reactive carboxylate ion is generated in sitv and that a low-boiling, nonaqueous solvent is employed, whereby the experimental procedure is considerably simplified. A related method has been reported which utilizes a hindered amine wdth dimethyl sulfate [Sulfuric acid, dimethyl csterj as the alkylating agent.9 The present procedure is carried out under somewhat milder conditions and avoids the use of highly toxic reagents. 

Normally in the production of diesters great effort is spent in obtaining high yields. Catalytic support of the esterification reaction and azeotropic distillation to remove reaction water yields diesters near 100% purity. The amount of unreacted educt material is usually very small. Following sulfation, in the presence of a hydrotrope to reduce viscosity, a 65% active content product with virtually no byproducts is obtained. 

Figure 6.17 Biocatalytic esterification in the presence of sodium sulfate as a drying agent.

R)-3-Phenoxybutanoic acid and the corresponding butyl (S)-ester were obtained by Burkholderia cepacia lipase-catalyzed enantioselective esterification of the racemic acid with 1-butanol in hexane containing anhydrous sodium sulfate to remove the water produced during the reaction (Figure 6.17) [64]. 

Numbers used in this cycle AG° for dissociation of sulfuric acid to sulfur tri-oxide AG° for hydrolysis of bis-p-nitrophenyl sulfate, estimated as described above AG° for hydrolysis of mono-p-nitrophenyl sulfate AG° for esterification to give pNP0S02, estimated as described above AG° for ionization of protonated SO3, estimated as described above AG° for ionization of p-nitrophenol. )... 

Out of the metal oxides, sulfated titania and tin oxide performed slightly better than the sulfated zirconia (SZ) catalyst and niobic acid (Nb205). However, SZ is cheaper and readily available on an industrial scale. Moreover, it is already applied in several industrial processes (7,8). Zirconia can be modified with sulfate ions to form a superacidic catalyst, depending on the treatment conditions (11-16). In our experiments, SZ showed high activity and selectivity for the esterification of fatty acids with a variety of alcohols, from 2-ethylhexanol to methanol. Increasing... 

Figure 33.2. Esterification of dodecanoic acid with methanol, using an alcohokacid ratio of 3 1 and sulfated zirconia (SZ) as catalyst.

These compounds contain the fragment R as an alkyl or aryl moiety. In other words, they result from the esterification of an alcohol or a phenol with nitrous acid, nitric acid, phosphoric acid, sulfuric acid, or sulfamic acid, respectively. Many of the esters to be examined in this chapter must be activated prior to eliciting their effects, e.g., the organic nitrites and nitrates, which act as donors of nitric oxide or an analogous molecule, and phosphates, which are activated by hydrolysis or even by phosphorylation (antiviral agents). Sulfates are very seldom active or used as prodrugs, but they have significance as metabolites and as industrial xenobiotics. 

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