Acids, Organic thioacetals

Miscellaneous Curing Reactions. Other functional groups can react with the thiol terminal groups of the polysulfides to cross-link the polymer chains and build molecular weight. For example, aldehydes can form thioacetals and water. Organic and inorganic acids or esters can form thioesters. Active dienes such as diacrylates can add to the thiols (3). Examples of these have been mentioned in the Hterature, but none have achieved... 

The above reactions in this section have been examples of addition alone or addition followed by elimination. Ligand reactions involving nucleophilic substitution are also known and these are of the dealkylation type. Lewis acids such as aluminum chloride or tin(IV) chloride have been used for many years in the selective demethylation of aromatic methyl ethers, where chelation is involved (Scheme 27). Similar cleavage of thioethers, specially using mercury(II) salts, is commonly used to remove thioacetal functions masking ketones (equation 27).104 In some cases, reactions of metal ions with thioether ligands result in isolation of complexes of the dealkylated organic moiety (equations 28 and 29).105-107... 

This reaction is widely utilised in organic synthesis, when carbonyl groups may be protected as the thioacetals or thioketals. Unlike acetals or ketals, the thio compounds do not undergo acid catalysed hydration, and may be used in acidic reaction conditions. The metal-directed hydrolysis is rationalised in terms of the soft-soft interaction of the sulfur with the metal cation, in contrast to the hard-soft interaction with a proton. Hydrolysis is readily achieved on treatment with aqueous mercury(n) or silver(i) salts. Once again, the... 

Wood acetylated with thioacetic acid showed resistance to decay and termites at low WPG around 12. The available information on pattern of substitution of hydroxyls during acetylation with acetic anhydride suggests substitution of lignin hydroxyls at low acetylation levels. Resistance to micro-organisms, particularly those consuming cellulose, even at low acetylation... 

Uses of the Sulphides of Phosphorus.—The pentasulphide of phosphorus is used to replace the oxygen of organic compounds by sulphur thus ethyl alcohol gives ethyl mercaptan, and acetic acid thioacetic acid.4 The reactions, however, are somewhat complex thus with ethyl alcohol the first product has been shown to be diethyl-dithiophosphate, SP(SH)(OEt)s, the mercaptan being produced by a secondary reaction.5 Phosphorus pentasulphide, boiling under atmospheric or other definite pressure, has been recommended for use in constant temperature baths in place of sulphur. The compound P4S3, which is one of the most stable sulphides in diy air, but resembles phosphorus in some respects, is used as a substitute for this element in the manufacture of matches.6... 

Sc(() l f) ( is an effective catalyst of the Mukaiyama aldol reaction in both aqueous and non-aqueous media (vide supra). Kobayashi et al. have reported that aqueous aldehydes as well as conventional aliphatic and aromatic aldehydes are directly and efficiently converted into aldols by the scandium catalyst [69]. In the presence of a surfactant, for example sodium dodecylsulfate (SDS) or Triton X-100, the Sc(OTf)3-catalyzed aldol reactions of SEE, KSA, and ketene silyl thioacetals can be performed successfully in water wifhout using any organic solvent (Sclieme 10.23) [72]. They also designed and prepared a new type of Lewis acid catalyst, scandium trisdodecylsulfate (STDS), for use instead of bofh Sc(OTf) and SDS [73]. The Lewis acid-surfactant combined catalyst (LASC) forms stable dispersion systems wifh organic substrates in water and accelerates fhe aldol reactions much more effectively in water fhan in organic solvents. Addition of a Bronsted acid such as HCl to fhe STDS-catalyzed system dramatically increases the reaction rate [74]. 

Synthesis of 3-Acetylthio-2-alkyl Alkanals. Piperidine (100 pL) was added to alkenals 5a-f (34 mmol) under nitrogen at 10 °C in separated cylinders of die Quest 205 apparatus. Thioacetic acid (3.68 mL, S1.6 mmol) was dien added d op-wise at 10 °C. Thereafter, the reaction mixture was stirred for another 18 h at room temperature. The mixture was diluted widi Et20 (10 mL), washed first with HCl (10 mL, 1 N) and then twice with a saturated NaHCOa solution (10 mL). The organic phases were dried over Na2S04. All these steps were carried out at the same time in the Quest 205. Then, the solvent was evaporated for each sample. The GC purity of the crude products was 50-90%, depending on the starting alkenal. In each case, a mixture of the two diastereomers was obtained. The detailed analytical description of the 3-acelylthio-2-alky-alkanals 6a-f has been reported elsewhere (//). 

Carbetoxy-3,4-diphenylthiophene-5-carboxylic acid 3.3 To a solution of t-BuOK [from 4.2 g K (0.11 g atom) and t-BuOH (100 ml.)] was added at 30°C benzil 1 (8.0 g 38 mmol) and diethyl thioacetate 2 (14.0 g 68 mmol). After 15 min stirring the mixture was acidified with 15% HCI (20 mL) and the alcohol removed in vacuum. The residue was extracted with Et20 and the organic layer was extracted with 2N ammonia (20 mL portions) until the aqueous layer gave no precipitation upon acidification. The combined ammonia extracts were heated to remove Et20 and acidified to give 12.4 g of 3 (93%), mp 205-210°C. 

Thioacetals and ketals are important protecting groups used in organic manipulations. The regeneration of carbonyl compounds by cleavage of acid and base-stable thioacetals and thioketals is a challenging task. Cleavage of thioacetals normally requires use of toxic heavy metals such as Ti +, Hg, Ag, Tl +, or uncom-... 

Weak organic acids Acetate, p-aminobenzoate, p-aminosalicylate, anthranilate, benzoate, butyrate, caprate, caproate, caprylate, m-chlorobenzoate, crotonate, formate, gentisate, heptanoate, p-hedro) benzoate, L-2-hydro3 -isocaproate, isobutyrate, isovalerate, 2-keto-isocaproate, 2-mercaptoacetate, p-nalidixate, m-nitrobenzoate, phenylacetate, phthalate, propionate, saccharin, salicylate, sorbate, thioacetate, thiosalicylate, valerate [747]... 

Kekule s first important work was carried out in London in the laboratory of Stenhouse in St. Bartholomew s Hospital. He found that phosphorus penta-sulphide gives thioacetic acid (the first known organic thioacid) with acetic... 

Akohols, Thiols, and Esters.—A review of organic sulphur chemistry includes the conversion of thioacetals of cyclic ketones into cycloalkanethiols by reaction with sodium in ammonia followed by acid. " ... 

Thioacetals are valuable intermediates for organic synthesis in their own right. For example, thioacetals are desulfurized by Raney nickel to give the corresponding hydrocarbon. This provides another path from an aldehyde or ketone to a methylene group that does not require either strong acid or strong base. Therefore, this method complements the Wolff—Kishner and Clemmensen reductions. 

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