Triethylborane (3) reacts with sulfuric acid to form the sulfate Et2BOS(O2)OBEt2 (1a), which can also be prepd. from (Et2B)2O (4a) and SO3. Sulfate 1a reacts with (C8H14B)2O (4b) to give the solid surface C8H14BOS(O2)OBC8H14 (1b) and 4a. Compd. 1b is also obtained by treating 4b with SO3. The reaction of 4a with sulfuric acid leads to the cryst. cyclic sulfate I (x-ray structure anal.). I is also available from triethylboroxin (5) on reaction with SO3. The diboroxanes 4a and 4b and H2SO4 form insol. 1:1 addn. complexes 4a.H2SO4 and 4b.H2SO4, which react on heating at about 60 Deg to yield the cyclic sulfates I and II resp.