The synthetic importance of ylids, particularly those of phosphoms and sulfur, guarantees them a place in every undergraduate teaching program. Ammonium-imines (I) are isoelectronic with nitrogen ylids (11) and the two species show similar reactivity (1); the relationship to the corresponding N-oxides (111, also isoelectronic) is less marked, but the reaction described here is interesting in that it demonstrates the generality of base-catalyzed rearrangements throughout the series (and, incidentally, provides a simple method of preparing some hitherto difficultly accessible trisub- stituted hydrazines from N,N-dimethylhydrazine, which is readily available).

\ e \ a e -N-N- -N-C- 1:~ / / I /

(1) (11) (111) The well-known Sommelet-Hauser and Stevens rear- rangements (of ylids (2 ) ) and the Meisenheimer rear- rangement (of amine oxides (2)) do not normally lend themselves to student experimentation: in contrast the reaction described below is carried out extremely easily and the whole sequence takes only a single practical session. N-Benzyl-N,N-dimethylhydrazinium salts (e.g., IV)

rearrange smoothly to the corresponding N-benzyl- N',N1-dimethylhydrazines (e.g., VI) both on treatment with potassamide in liquid ammonia and photochem- ically in aqueous alkaline solution (3). An even simpler procedure has recently been reported (4) and this forms the basis of the experiment described here.

Me

D. Maytum and 8. R. T. Keene

Medwoy and Maidstone College of Technology Chotham, Kent, England

I e CeH5CHsBr + MmNNH, - CeH6CHzN-NH1

I -

Me Br- +

(IW Me l m e

MmNNHCH3CsHs - CsHsCHzN-NH I Me

(VI) (V) The reaction between benzyl bromide and N,N-

dimethylhydrazine [CAUTION: occasionally re- ported to cause skiu-irritation] provides an interesting demonstration of the superior nucleophilicity of the tertiary nitrogen atom: the 100 MHz pmr spectrum of the precipitated salt in DMSO-d6 shows it to be essentially pure (IV), with sharp singlets at 7 6.70(6H), 5.20(2H) and 3.83(2H) arising from the +N(CH&, CH2, and NH2 protons, respectively. The remaining (aromatic) protons appear as an unresolved multiplet centered at .r 2.42(5H). Heating with powdered potassium hydroxide produces (VI) in good yield, presumably via the ylid (V) since removal of a benzylic proton will not compete effectively with loss of the more acidic amino proton. A radical mechanism has

The Rearrangement of N-Ben~yl-N,N-dimethylhydrazini~m Salts

been proposed (4) for this rearrangement, largely by analogy with the closely related Meisenheimer and Steven reactions, for which radical pathways have recently been established (5, 6).

The experiment lends itself to extension as a simple student project in that substituted-benzyl-dimethyl- hydrazinium salts can be made to rearrange similarly, although the simple thermal procedure described here is reported to fail with, for example, nitro-substituted compounds because of easy (in some cases violent) oxidation of the -NH-CH- system (4). The major product when N-p-nitrobenzyl-N,N-dimethyl- hydrazinium bromide is rearranged photochemically, or with potassimide in liquid ammonia, is 4,4'-dinitro- bibenzyl (3). This provides both interesting confirma- tion of the radical nature of the process, (in this instance a t least) and a more plausible explanation of the violence of the thermal process in cases where radical formation is much more facile. Experimental Procedures

A solution of N,N-dimethylhydrazine (12.0 g, 0.20 mole) in sodium-dry benzene (50 rnl) is cooled to 0°C and benzyl bromide (17.1 g, 0.10 mole) is added drop- wise with stirring or shaking, keeping the temperature below 5'C during the addition. The hydrazinium salt forms immediately, and after stirring for a short while at O°C the solid is collected, washed with benzene to remove unchanged N,N-dimethylhydrazine and dried at 80°C. The yield of N-benzyl-N,N-dimethylhy- drazinium bromide, mp 147-8'C (lit. 4 148-9'C) is 22.5 g (97.573. This material is sufficiently pure to be used directly: if required it can be crystallized from ethanol-ether.

The hydrazinium salt (11.55 g, 0.05 mole) is mixed thoroughly with finely-powdered potassium hydroxide (7.0 g, 0.125 mole) and the mixture is placed in the bulb of a Vigreux flask equipped for distillation under reduced pressure. On gentle heating under vacuum the product distils over as a clear, mobile liquid, boiling range 100-110' at 23 mm Hg: infrared examination reveals the presence of an appreciable amount of water, which can be removed by taking the distillate up in ether, drying the solution over sodium sulfate, and then redistilling. The student yield of pure N-henzyl-N1,N'-dimethylhydrazine, hp 82-84' at 1.5 mm Hg (lit. (4) 102-3°C at 23 mm Hg), is 6.0 g (80%). Literature Cited ~... (1) Joxamnr. A. W., "Ylid Chemistry." Acad. Press, New York. 1966. (21 COULD. E. S.. "Mech&nirm and Structure in Organic Chemistry," Holt.

Rinehart. and Winaton Ine., New York. 1959. (3) Honsorr. H., KEENS, B. R. T., AND MATTUM. n., to be published. (4) Koaro, K., AND ZEEW, B., Chem.Ber., 103,2052 (1970). (51 S c n o ~ ~ r o ~ r , U., m o Lnowro, U. , Chmm. Bar.. 101, 2224 (1968); with

PIT~CH. M.. m n FBA~ULEN. W.. Liehiaa Ann. Chem.. 703,77 (1967). (6) SCH~.L&PP. 'u.. LUDWIG. il., O S T E ~ ~ N N , G . , AND PATBCR, M.,

Tet~~hsdion Lell., 3415 (1969).

Volume 49, Number 3, March 1972 / 21 5