H. J. den Hertog

Bromination of pyridine-N-oxide in fuming sulphuric acid

Abstract Pyridine-N-oxide has been brominated with a mixture of bromine and fuming sulphuric acid. 3-Bromopyridine-N-oxide is formed as the chief product together with 2,5- and 3,4-dibromo-pyridine-N-oxide in about equal amounts and small quantities of 2-bromopyridine-N-oxide and 2,3-dibromopyridine-N-oxide. The mechanism of this reaction is discussed in relation to the bromination of pyridine-N-oxide with a mixture of bromine, 90% sulphuric acid and silver sulphate, which yields only a small amount of 2- and 4-bromopyridine-N-oxide. 3 In this connection the bromination of the isomeric monobromopyridine-N-oxides in both media has been investigated.

The synthesis of 4H-pyran containing hemispherands via pyrylium salts

Two new hemispherands 2a and 2b containing a central 4H-pyran unit were synthesized via appropiately substituted 2,6-phenyl pyrylium salts; largest ΔGo values of complexation of 2a and 2b with different alkali picrates are found for Na+ and K+.

A nesting conformation of the 5′-bromo-1′,3′-xylyl-18-crown-5·tert-butylammonium hexafluorophosphate complex; the correlation of the structures of crown ether complexes in the solid state and in solution

Single-crystal X-ray analysis of the 5′-bromo-1′,3′-xylyl-18-crown-5· tert-butylammonium hexafluorophosphate complex shows that the complex is of the “nesting” type in which the cation and the aryl group are on the same face of the macroring and that the macroring has a (ag+a) (ag−a) (ag+a) (ag−a)(ag+a) (ag−a) conformation.