1222
LAMAR [CONTRIBUTION FROM
THE
F I E L D AND
P.4UL H.
SETTLAGE
Vol. 76
DEPARTMENT OF CHEMISTRY OF YANDERBILT UNIVERSITYJ
Alkanesulfonic Acid Anhydrides1 BY LAMAR FIELDAND PAULH. SETTLAGE RECEIVED SEPTEMBER 28, 1953 Methanesulfonic anhydride ( I ) and ethanesulfoiiic anhydride (11), chosen as reasonably representative alkanesulfonic anhydrides, were prepared from the corresponding acids by means of phosphorus pentoxide. I and 11, as well as p-toluenesulfonic anhydride (111), were also prepared from the corresponding sulfonyl chlorides by the use of metallic oxides. I reacts more rapidly than does methanesulfonyl chloride ( I V ) in sulfone formation with benzene, and forms methanesulfonyl isocyanate in much better yield (38%) than does IV (570). Results with I and I V are seemingly similar in the sulfonylation of diethyl malonate. I resembles trifluoroacetic anhydride in promoting esterification of acetic and benzoic acids. Other reactions of I are also discussed, including those with pyridine and phenylmagnesium bromide.
A previous communication* from this Laboratory described the conversion of representative aromatic sulfonic acids to the corresponding anhydrides by means of phosphorus pentoxide, and dealt with several aspects of the chemistry of these anh y d r i d e ~ . ~The present paper reports an extension of these studies, particularly with reference to alkanesulfonic acid anhydrides. Methanesulfonic anhydride (I) and ethanesulfonic anhydride (11) were prepared in the manner reported2 for benzenesulfonic and @-toluenesulfonic anhydride (111), but under milder conditions. Treatment of methanesulfonic acid with acetic anhydride or isopropenyl acetate6 did not yield I, suggesting that the bond-strength relations involved in formation of I are unfavorable in these instances. Alkanesulfonic anhydrides, as exemplified by I and 11, are seemingly best purified by distillation, and subsequent recrystallization when feasible. 111, however, decomposes partially during distillation, so that recrystallization alone is preferable. The identity of I was established by mixture m.p. with authentic material,7 and was confirmed for both I and I1 by conventional methods. Sulfonyl chlorides are frequently more easily accessible than the sulfonic acids. X direct synthesis of anhydrides from the chlorides accordingly appeared to deserve investigation. Carboxylic anhydrides may be obtained from acyl chlorides by reaction with pyridine and, subsequently, with water,8 (1) Abstracted mainly from t h e Ph.D. thesis of Paul H. Settlage, September, 1953. (2) L. Field, THISJ O U R N A L , 74, 394 (1952). (3) A noteworthy addition t o previously summarized2 preparations of sulfonic anhydrides has been contributed recently by Khorana,4 who obtained anhydrides from sulfonic acids h y using substituted carbodiimides (RN = C = XR). This apparently general reaction seems especially promising f o r use with valuablr sulfonic acids, where t h e use of a less direct and more expensive route is expedient. T h e preparation of aromatic sulfonic anhydrides from the acids by t h e use of thionyl chloride is well known (see ref. 3 for citations). I n contrast, methanesulfonic acid has seemingly given o n l y t h e chloride. It is accordingly noteworthy t h a t in one instance our use of thionyl chluride in a well-established procedure5 gave t h e chloride in only abaut 23% yield, b u t t h e anhydride in 07% yield (m.p. 60.5-64'). NOTE ADDED I N PROOF: L. N. Owen and S. P. Whitelaw [ J . C h o n . SOC., 3723 (1953)] recently have reported t h a t methanesulfonic anhydride m a y be prepared in 82y0 yield by heating t h e acid with thionyl chloride. These authors also pointed o u t t h a t use of t h e anhydride, rather than the chloride, may h e advantageous in the preparation of certain types of methanesulfouates, in agreement with o u r coriclusion t h a t t h e anhydride may be preferable in special instances. (1) 1%.G. lihurana, C C L IjZ,. C h e m . , 31, 23.5 (19>3), ( 5 ) C . R . Koller and P. J. Iiearsi, Trirs J O I . K N A I . , 70, ?.!l.>: !lO4S), O r i . . S y i f t h e s e c , 3 0 , 5 8 (lYS0). (0) Kindly providrtl by Tenoe'jsee l i ~ s t n i a nCcwi., Kingsport. 'l'enn ( i ! 0 . 0.Rilleter, I ~ c , ; . 3, 8 , 2013 !1003) ( 8 ) I1 h i l k i n s and Q 15. Thumpson, 'Trrrs J O L ' R S A L , 71,2242 (1
