Paper ionophoresis of amino compounds. Formation of carbamates, and related reaction

Abstract

Carbamates (N-carboxy derivatives) are formed when solutions of primary or secondary amino compounds in strong alkali are exposed on paper strips to carbon dioxide, and may be separated by paper ionophoresis and detected as additional, anionic components. The formation of mono-, di-, tricarbamates, and so on, from a polyamino compound occurs concurrently, and when an amino compound containing n reactive groups is submitted to paper ionophoresis in 0.lN sodium hydroxide at 18-20° after exposure to carbon dioxide, it affords n additional spots. Most primary and secondary amino groups in saturated compounds, and some aromatic amino groups, are reactive, but highly hindered amino groups are not. Some unreactive groups become reactive when the ionophoresis is conducted at 1-2°. The procedure is analytically useful, and may be used to gain information about the structure of amino compounds. The conditions favouring the formation of carbamates have been defined by paper ionophoresis. The primary reaction in the formation of carbamates is the addition of carbon dioxide to the amino nitrogen atom; carbamates are not formed directly from the carbonate ion. The rate of reaction with carbon dioxide and the stability of the carbamates may be correlated with the steric and electronic environment of the amino groups. Low temperature and high alkalinity are essential for the stability of carbamates in solution. The "basic mercury carbamates" described by Neuberg and Kerb (Biochem. Z., 1912, 40, 498) do not seem to have the structure assigned by these authors. Dithiocarbamates obtained by reaction of amines with carbon disulphide in alkaline solution are easily identified by paper ionophoresis, but they cannot readily be formed on the paper strip. Attempts to prepare N-sulphinates by reaction of amino compounds with sulphur dioxide on paper strips have been unsuccessful.