Formic acid from acetylene

The Reppe hydrocarboxylation of acetylenes was initially carried out in the presence of an acid, but little was known about the function of the acid or the nature of the carbon monoxide transfer agent. Sternberg et al. found that diphenylacetylene can be hydrocarboxylated in alkaline solution and that in this case a nickel carbonyl anion is the source of carbon monoxide. When the hydrocarbon was shaken with a saturated solution of sodium hydroxide in methanol in the presence of excess nickel carbonyl under helium the reaction mixture turned dark red. After 80 hrs., acidification and workup aiforded a-phenyl-rru/is-cinnamic acid and 1,2,3,4-tetraphenyl-butadiene in the yields indicated. Note that the ciimamic acid results from cis addition of the elements of formic acid. 

Removal of blocking groups. Regeneration of aldehydes from their acetals can be accomplished by refluxing in formic acid for 10-60 min.17 The reaction is applicable to sensitive aldehydes, such as a-acetylenic aldehydes. 

The action of ozone on acetylene is very violent and explosions result when the reaction is conducted in the vapor phase. However, it is possible to study the mechanism of the reaction by carrying out the ozonization in solution. The ozonide formed in this way is too unstable to be isolated and only by allowing a very slow decomposition to occur by slow evaporation of the solvent is it possible to isolate reaction products. In this way, it has been found that the material remaining after evaporation of the solvent consists of a large proportion of glyoxal (SI per cent) and a small amount of formic acid (5.6 per cent).1,12 The decomposition of the ozonide of acetylene differs from that of ethylene in that the linkage of carbon to carbon is not destroyed. The direct oxidation of acetylene with ozone, however, results in die formation oi formic acid and carbon dioxide.188... 

Sporadic reports of stereoselectivity in such cyclizations appear, notably in the work of Noza-ki116-117 and a report from Witteveen and van der Weerdt118. For example, treatment of the chiral acetylenic diol 5 in hot formic acid affords the cyclopentenone 6 in modest yield. 

Enol formates, which are formylating agents under neutral conditions, are obtained from 1-alkynes and formic acid by arene-ruthenium(II) catalysis Heating acetylenes (phenylacetylene, diphenylacetylene, 1-octyne or 4-octyne) with formic acid to 100°C produces ketones and carbon monoxide. It was shown by NMR spectroscopy that the process involves the intermediate formation of enol formates (equation 35). Treatment of terminal alkynes with carbon dioxide and secondary amines in the presence of a ruthenium catalyst affords vinyl carbamates, e.g. equation 36 d88. reviews, see References 189 and 190. 

From o-Aminobenzenethiols (Type A S—C H4—N + C).—An improvement on the standard procedures (milder conditions) is the use of DMF dimethyl acetal instead of formic acid or alkyl orthoformates. A 64% yield of benzothiazolin-2-one is obtained when o-aminobenzenethiol is treated sequentially with carbon monoxide and oxygen in the presence of triethylamine and selenium in DMF. o-Aminobenzenethiol forms substituted vinylamine adducts with acetylenic nitriles RC=CCN. These cyclize in the presence of sodium ethoxide, and the products lose acetonitrile on distillation at atmospheric pressure to give 2-sub-... 

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