1754
COMhlUNICATIONS TO
nitride by heating urea and boric acid appears implausible. However, when this BNO residue is heated in a stream of ammonia over the temperature range 30i)-050°, it is nitrided, with the simultaneous formation and removal of water, to give a relatively pure boron nitride (residue a t 9 X o , 13.639; urea and boric acid reactants. .Inal. B, 4:2.9; S , 34.2). This nitridation is significant in t h a t the rate of nitridation progressively increases over the temperature range of 50i)-95ilo. This is in contrast to currently favored routes where a viscous boric oxide liquid on a preformed boron nitride or a calcium phosphate support shows slower rates of nitridation. This latter process is substantially unaxected by increasing temperatures over this tcmperature range. The final traces of oxide impurity may be removed from the boron nitride product by reaction with ammonia a t higher temperatures or by heating in a nitrogen stream to l&50°, where the oxide impurity volatilizes (analysis B , 44.2; S , X.0). ' A% wide range of nitrogenous materials may be substituted for urea in this reaction scheme, such as biuret, guanidine, cyanamide, dicyandiamide, thiourea, ammelide, and melamine. T h e nitrogen contents of the solid intermediates and the final products show some variations, but the products obtained using cyanamide, dicyandiamide or guanicline are comparable or superior to that obtained using urea. In cooperation with N. E. \Veston and J . Thomas. Jr., in a paper to be published in the J . Am. C h m . SOL.,a turbostatic structure has been found for R N prepared from urea-boric acid and ammonia; a transformation of this structure to the ordered layer lattice occurs. a process which is unexpectedly promoted by boron oxide impurities.
Yol. s4
THE E D I T O R
consequence of thermally induced prototropic isomerization to the propenyl thiophenyl ether (V) and no more than a trace of o-allylthiophenol (11) was found. This result has been attributed to the (assumed) inability to form the dienone intermediate (IX), analogous to that which has been established6' for the Claisen oxyether rearrangement (path A) because of the recognized weakness of the
\
x
bond in C=S and the instabil-
/
ity of x links composed of other than electronss.
v
H
L
valence
I
H .1
IIa
I11
IIIa
(10) T o whom a11 inquiries shiiuld be sent at S a t i o n a l Institutes of H e a l t h , Bethesda. RIaryland.
DIVISION 'r. E. ISDUSTRIAL & BIOCHEMICALS DEPT. E. I. DU POSTDE SEMOURS & Co., INC. ~VILMISGTOS, DELAWARE RECEIVED FEBRUARY 22, 1962 RESEARCH
O'CONSOR~O
T H E CLAISEN REARRANGEMENT OF ALLYL ARYL SULFIDES
Sir: Failure to produce Claisen rearrangement of allyl thiophenyl ether (I) under conditions' which can readily effect the rearrangement of the corresponding oxyethers a t reasonable rates'.3 has been noted recently..' The Russian authors of this report have stated t h a t the principal product of the reaction studied earlier by Hurd and Greengard" was the (1) For a f u l l discussion of this reaction see D. S. Tarbell i n R . Adams. "Organic Reactions," John R'iley and Sons, I n c . , S e w Y o r k , X . Y . l'ol. , 11, 1944, C h a p t e r I. (2) \V. K. W h i t e , I). G w y n n , K . S c h l i t t , C. Girard and I\', Fife, J , A m . C h m z . So
