The synthesis and X-ray structure determination of N, N'-di (o-tolyl) piperazine N, N'-dioxide tetrahydrate, I, N, N'-di (p-tolyl) piperazine N, N'-dioxide tetrahydrate, II, and N, N'-di (p- chlorophenyl) piperazine N, N'-dioxide tetrahydrate, III, are described. Compound I