Thioacetic anhydride

The Group 2 thioacetate compounds, M(SOCMe)2L, have been studied as single-source precursors for the formation of binary Group 2 metal sulfides, MS. The rationale to investigate these compounds is that if the reaction pathway involves thermally induced elimination of thioacetic anhydride according to Eq. (32), then the metal sulfide film should be relatively pure. 

Figure 20 1 shows the structures of various derivatives of acetic acid (acetyl chlo ride acetic anhydride ethyl thioacetate ethyl acetate and acetamide) arranged m order... 

C=0)-halogen, 0-(C=0)-halogen, S02-halogen, N=C=0, N=C=S, N-C(=S)-N Acyclic C(=0)-S, acyclic C(=S)-0, acyclic N=C=N Anhydride, aziridine, epoxide, ortho ester, nitroso Quaternary amines, methylene, isonitrile Acetals, thioacetal, N-C-O acetals Nitro group, >1 chlorine atom... 

Quinazolin-2-ylmethyl)thioacetic acid (600) gave the l,4 thiazino[4,3-a]-quinazoline (601) when heated with acetic anhydride and pyridine [88IJC(B)578],... 

An interesting reaction is that of the mononuclear [W(CO)5(SH)] and the SH- -bridged dinu-clear /i-HS W(CO)s complexes with acetic anhydride to give the thioacetate complex [(MeCOS)W(CO)5]. The SH complexes react with aliphatic ketones and aromatic aldehydes to yield the complexes [(R2C=S)W(CO)5] and [(RCHS)W(CO)s] of these otherwise unstable thioketones and thioaldehydes.142... 

Disulfides, diselenides, and ditellurides can be oxidized by hypervalent iodine compounds quite easily. Depending on the reaction conditions disulfides can be oxidized to sulfinic esters [59] or thiosulfonic S-esters [60,61]. Diselenides can be transformed into selenosulfonates [62]. Arenetellurinic mixed anhydrides are mild oxidants and can be obtained by oxidation of the corresponding ditellurides as shown in Scheme 9 [63]. Recently it was shown that a thioacetal based linker for solid-phase synthesis can be cleaved oxidatively using [bis(trifluoro-acetoxy)iodo]benzene 4 [64]. 

In view of the expected instability of the mercapto aldehydes likely to be formed, the reaction mixture was extracted and the concentrated extract treated with LiAlH / acetic anhydride/pyridine. The acetates/ thioacetates isolated from this reaction mixture were analyzed with MS/NMR spectroscopy. From the results of these analyses, the reaction routes as indicated in Figure g are followed. 

Figure 1. Vapor phase acetylation assembly. Key 1, reaction chamber 2, wood samples 3, thioacetic acid 4, thermometer 5, water condenser 6, heating mantle 7, magnetic stirrer with heater and 8, acetic anhydride and catalysts.

Effect of Wood Moisture. It has been recommended that for acetylation with acetic anhydride, the moisture content of wood should be about 2% as excess moisture is likely to react with acetic anhydride and produce acetic acid (37). Goldstein et al. (28) observed that raising the moisture to 22% considerably slowed the reaction and each 1 percent of moisture in wood would lead to hydrolysis of about 5.7% acetic anhydride. Low moisture contents are not possible to attain in commercial treatment of wood. With ketene gas it has been possible to acetylate wood with as high as 20% moisture content with WPG about 25% (40). Thioacetic acid is only partially stable in cold water and dissociates at higher temperatures. The presence of moisture in wood could thus be critical in treatments with thioacetic acid also. Results of mango treated at 5 different moisture levels are depicted in Figure 3. As may be seen a moisture content up to 7.5% has no adverse effect on WPG. At 10% moisture content the WPG decreased to 4.6. With further increase in moisture, there was a gradual decrease in WPG attained. 

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... 

Nitration and oxidation. Clay-supported Cu(N03)2, unlike clayfen (12,231), > shelf-stable for months. Like clayfen, it is a convenient source of N02+ and can leave thioacetals or selenoacetals to the carbonyl compound at 25° in high yield. It effects aromatization of 1,4-dihydropyridines in 80-92% yield. In the presence i acetic anhydride, it can effect nitration even of halobenzenes at 25° with marked, - jra-preference, which can be enhanced by use of lower temperatures. 

Treatment of the 2-pyrrolyl allyl thioether (498) with acetic anhydride and quinoline at 170 °C (or in A jV-dimethylaniline at ca. 100 °C) results in a thio-Claisen rearrangement to give the 5-(3-allyl-2-pyrrolyl) thioacetate (499), whilst peracid oxidation of (498) produces the non-rearranged sulfone in low yield and Raney nickel reduction of (498) yields 3-propylpyrrole (78CJC221). The polyphosphoric acid-catalyzed cyclization of (2-pyrrolylthio) acetic acid (501 R = R = H) somewhat unexpectedly yields (502) via the Spiro intermediate, instead of forming the expected oxothiolane (500), which can be obtained by a Dieckmann cyclization of ethyl (3-ethoxycarbonyl-2-pyrrolylthio) acetate (501 R = Et, R = C02Et) (B-77MI30506). 

The lactamization of A-(5,5-diphenyl-4-oxo-2-imidazolyl)glycine 41 to 6,6-diphenyl-l,6-dihydroimidazo[l,2-tf] imidazole-3,5-dione 42 (Scheme 28) and the conversion of 2-thioacetic acid derivative 43 into the respective imidazo[2,l-A thiazole-3,5-dione 44 can be induced by treatment with DCG or acetic anhydride (Schemes 28 and 29) C1997AP85, 2000PHA429, 2001JST(597)73, CHEC-III(11.04.9.1.4)159>. 

A similar mechanism has also been proposed for deprotection of S,S -thioacetals using seleninic anhydride/ ... 

Interestingly the allenic thioacetal (123) was obtained from the a-hy-droxythioacetal (122). ° The diphenylseleninic anhydride oxidation of 3/3-t-butyltellurocarbonyloxy-5a-cholestane (124) provided the ester (125) whereas reduction with NaHTe gave the ether (126) and the dimeric ether (127). ° ... 

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