Diethyl thiocarbonate

Figure 4.36 shows the UV absorbance spectra of diethyl dixanthogen (EX)2, diethyl monothiocarbonate (MTC ) and diethyl thiocarbonate (EPX). The UV adsorption peaks of (EX)2 lie in about 238 nm (strong) and 286 nm (weak). The ratio of adsorption intensity of two peaks is 2. UV peak of MTC lies in about 225 nm (strong), EPX lies in about 348 nm (strong) and 221 nth (weak). 

Surprisingly, the reaction of diethyl carbonate and 0,0 -diethyl thiocarbonate with lithium bis(trimethylsilyl)phosphanide has been found to give ethoxy trimethylsilane and the phosphaalkynes (dme)2Li-0-CsP and [(dme)3Li] [S-CsP] respectively. As known so far, lithoxymethylidynephosphane shows a great tendency to undergo [2+2] cycloaddition and reduction reactions. The NMR parameters of the [S-C=P] -anion resemble much more the values of diorganylamino-phosphaalkynes than those of its oxygen homologue. 

Modification of this synthesis can be achieved by treating the hydrazide with diethyl carbonate or diethyl thiocarbonate. In the latter case the products are 5-thiono-3-pyrazolidinones. 

DiiNES et al. [16] have identified the products formed by inter-molecular rearrangement of thiocarbonate esters on heating. They were thus able to elucidate the mechanism of the reaction. They used loose layers of alumina (activity III according to Bbockmann) and chloroform-carbon tetrachloride-diethyl ether (30 + 30 + 40) as solvent. 

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