March 5, 1958
RATEOF
[CONTRIBUTION K O . 1468 FROM
Quaternization Kinetics.
V.
QUATERNIZATION OF DI-t-.4MIKES
THE STERLING
1095
CHEMISTRY LABORATORY O F YALE UNIVERSITY]
Di-tertiary Amines with Butyl Bromide in Propylene Carbonatel
B Y LEE-YUNG CHOW2s3 AND
RAYMOND
A I . FUOSS
RECEIVED SEPTEMBER 26, 1957
I. Rate constants at 25 and 50' for the quaternization by n-butyl bromide in propylene carbonate (dielectric constant 65) of the following amines were determined: Me2N.C6H6, p-Me2S.C8H4Me,P,p'-MezT.CgHI.CH2.CsH4.SMez, 4,4'-CbH4-
X(CH2))C6HIN,4,~'-CSHa-U(CH2)2C6H,S anc! C5H4NCH=CHCsH4K. The rate of quaternization of the second nitrogen in the diamines is always less (about 0.5-0.7) than t h a t of the first. The decrease is ascribed primarily t o a n electrostatic field effect rather than to a n intramolecular shift of electron density. 11. The main reaction product of dimethylaniline and butyl bromide in solvents of low dielectric constant is trirnethylphenylammonium bromide. Molecular decomposition of the expected primary addition product into methyl bromide and methylbutylaniline accounts for the result. 111. The deceleration of the rate of quaternization of poly-4-vinylpyridine as the reaction proceeds is a consequence of electrostatic effects and not of the polymer structure per se.
Introduction The rate of quaternization of pyridine and 4in a variety of solvents has been studied as a preliminary to attacking the problem of the peculiar behavior of poly-4-vinylpyridine on quaternization.' The latter begins to quaternize a t a normal rate, but the rate begins to decrease markedly after about half of the pyridine nitrogens have been quaternized. This behavior might be ascribed to one of (at least) three causes: (a) intramolecular electronic effects of quaternized neighbors located on the polymer chain; (b) extramolecular electrostatic field effects of quaternized neighbors; or (c) high local concentration of pyridine groups in the centers of polymer coils. The experiments presented in this paper were designed to test these hypotheses: our conclusion is that hypothesis (c) is excluded and that hypothesis (b) is probably correct. The poly-4-vinylpyridine chain has the repeated structure -CHX,CHPy.CH2.CHPy.CH*-
Obviously 1,3-di-(4-pyridyl)-propane is the simplest model substance which can represent a segment of the chain, as far as effects of neighboring groups are concerned. We have found that the rate of quaternization of the second nitrogen in 4,4'-Py(CHz),Py is only about 7Oy0 of that of the first; consequently, the deceleration observed in the polymer does not depend primarily on the fact that the 4-pyridyl groups are attached to a polymer chain. Furthermore, the rate constants for the second quaternization of 1,3-dipyridylpropane and 1,3-dipyridylethane are so nearly alike (3.3 X and 2.8 X that an intramolecular inductive effect can hardly be considered as the cause of the decrease from the rate constant for the (1) Technical Report No. 55 submitted t o t h e Office of Naval Research. Reproduction of this paper in whole or in p a r t is permitted for a n y purpose of t h e United States Government. (2) ONR Research Assistantship, F r a n k M. Shu Scientific Fellowship (China Institute in America) and American Cyanamid Scholarship are gratefully acknowledged. (3) Results presented in this paper are based on a dissertation presented by Miss Lue-Yung Chow t o the Graduate School of Yale University in partial fulfillment of t h e requirements for t h e Degree of Doctor of Philosophy, June. 1957. ( 4 ) P. L. Kronick and R. h f . Fuoss, THISJ O U R N A L , 7 7 , 6114 (1955). ( S ) E. Hirsch and R . AT. Fuoss, ibid., 7 7 , 6115 (1955). ( 6 ) M . Watanabc and R . M. Fuoss, ibid.. 7 8 , 527 (1956). ( 7 ) B. Coleman and R. hi. Fuoss, i b i d . , 7 7 , 5472 (1955).
first quaternization (4 to 5 x 10-4, practically equal to that for -?-picoline), Comparison of these rates with those for two other model substances PyCH=CHPy and p,p'-~lez?\J.CsH4.CH1.C)eH4.KMe2 suggests that the decrease probably is due to an extramolecular electrostatic field effect produced by the positive charge on the first nitrogen. Experimental Materials.--Propylene carbonate (Jefferson (!hemica1 Co.) was redistilled; the middle cut (111-114' at 12 mm.) was used. Butyl bromide was redistilled. p,p'-Methylenebis-( S,N-dimeth~-aniline)was recrystallized twice from 95% ethanol after decolorizing with charcoal; approx. sohbility in boiling ethanol, 8 g./lOO cc., m.p. 89.5". p,p'Bis-(dimethj-lamino)-benzophenonewas recrystallized from 95y0 ethanol; solubility, 4 g.j1OO cc.; m.p. 175'. Dimethylaniline was first purified by two fractional f:reezings, decanting and discarding about one-half each t i n e . The final crystals were allowed to melt; the liquid was dried overnight with anhydrous calcium sulfate and then distilled under reduced pressure using nitrogen. 1,3-Di-(?-pyridyl)-propanewas prepared by the -4ldrich Chemical Company, by reaction between dimethoxymethane and 4-picoline.* I t was recrystallized from 5: 1 n-hexane-benzene: 6.5 g. as first crop were recovered from 10 g. in 150 cc. of mixed solvent; m.p. 60.5-61.5". 1,2-Di-(4pyridyl)-ethane also TYas prepared bJ- -1ldrich; i t was recrystallized from 3 : 1 cyclohexane-benzene (approx. s o h bility, 7.5 g./lOO cc.). The spectrum9 shom-ed negligible absorption a t 299 atid at 289 mp, indicating absence of the corresponding ethylene from which i t was prepared by hydrogenation, using charcoal supported palladium as catalyst. *ildrich 1,2-di-(4-pyridyl)-ethylenemas recr)-stallized from mater; solubility, 1.6 g./lOO cc. a t 100'; m . p . 153154". \Ye take this opportunity to thank Dr. Xlfrttd Bader of the Aldrich Chemical Companh-, Inc. (Milwaukee, \Visconsin), for his helpful cooperation in the synthesis of the above compounds and for the information t h a t the ethylene is the trans-derivative. Method.-Solutions were prepared b!- weight and sealed into anipoules which were then placed in thermostats at 25' (or 50'). At appropriate intervals, bromide ion content was determined potentiometrically, using 0.005 iV silver nitrate solution. Details of procedure already have been described.' An interesting side problem arose from plans to check the rate of quaternization by conductimetric methctds; we started by attempting to synthesize dimethylbutylphenylammonium bromide from butyl bromide and dimethylaniline, both by heating the two reagents together undiluted and in acetone solution. The yield was poor, in contrast to the usual nearly quantitative course of quaternization reactions. The recr!-stallized products (m.p. 216-217') analyzed to 37.04% Br, us. 30.95% expected! Elementary
____--
(8) A. Ladenhurg, B c r . , 21, 3099 (1886). (9) M. Yamin and R. M. Fuoss, THISJOURNAL, 76, 48'30(1953); E. D. Bergmann, F. E. Crane, J r . , and R . 11, Fuoss. ibid , 74, 5979 (1952).
aiialysis (Schwarzkopf) gave tlie following results: C, 50.32, 50.49; H , 6.75, 6.60; N , 7.01, 7.20. Freshinan cheinistry applied t o these figures suggested t h a t our product was trimethylphenylaInnioniurn bromide. \'orliinder and Siebert'o report 214' as the melting point of hle3NPli.Br and 110-115° for the correspondiiig nitrate. 1I.e accordingly converted a sample of our broniitle t o nitrate by metathesis in aqueous solution with silver nitrate. The product on purification melted a t 123-127"; considering the 5" spread on the earlier melting poiiit, we felt reasonably certain t h a t our product was indeed R.le&PhBr. \Ye therefore prepared the latter salt by addition of methyl bromide to dimethylaniline ill acetone solution. The product was recrystallized from sac-butyl alcohol; its infrared spectrum was then taken in chloroforin solution. T h e fiugerprint region is shown iti Fig. 1B. Curve C of tlie s:me figure is the spectrum of the product obtained from BuBr a n d MeniYPh; there can be no doubt t h a t these reagents produce the trimethylpheuyl salt.
it should be possible to obtain ilfeaNPliBr froin this salt by treatment with Ille2KPh. The butyldimethyl salt is rnucii more soluble in :icetone than the trirneth>.l salt. \Ve therefore mixed the butyldirnetli>-l salt and dii~ieth>.laniliiie (0.0058 mole escli) iii 20 cc. of acetone; no precipitate appeared in one day :it room temperature but after 1 d:t)-s a t 50" (sealed tube), crystals appeared. Their spectruni is s h o m iii Fig. 1 9 , which identifies them as MeaNP1iBr. The filtrate gave on evaporatioii a high boiling liquid wliose spectrum is shown in Fig. 2C. Coinparison with tlic I
II
A ,-
-- -. - .- . -. .- ..-. __ ,
r~~
~
I
8
---
- ..____.-.__._i
,
Fig. 2.-Iufrarctl
~
L--
Fig. l.-Iiifrared
~. . . ~
-
spectra o f salts.
\\'e
nest investigated tlie atltlitiini of iiictliyl broiiiitle 11, lilethylbut~-iaiiiliiie; the latter \vas jircl)aretl by tlie nicsthotl uf Reilly and Hickiiibottorii." (Since the c s l x c t c t l iiiipurity in the AleBuNPh would be meth>-laniline,the p r i d uct was treated with phenyl isucyanate to remove i t . ) The purified amiiie was treated with triethyl broniide ill acetone solution; the solid which separated (85yo yield) analyzed t o 31.07, 31.04yo Rr, in excellent agreement with t h e value calculated for Me2BuSPhBr. The itifrareti spectrum is shown in Fig. 111; it is, of course, markedly different from t h a t of AfeaNPhBr. These experiments thus show t h a t MeBr adds norinally to MeBuNPh but t h a t BuBr gives an abnornial ,find product with Me2KPli. Since several of our kinetic stuiiies on the addition of BuBr t o aryl amines had already been completed, it obvious1.v became necessary t o learn whether the inilicil product of BuBr addition was normal and whether this reaction controlled t h e rate of production of bromine ion. Iiicideiitally, dimethyltoluidine and butyl bromide also give the trimethj-l salt: the addition product ana ed t o 34.82','$ Br; calcalculated for hfe7S?'1culated for BuYic2NT1Gr, 29.34 Br, 34.72%. I f BuMe~NI'liHr is the i i i i t i d l protluct ilf t l i v r e a c i o i i , _____ (10) I ) . V u r l i i d c r aiid li. S i e l x r t , Leu., 62, 2h.l ( 1 9 1 ! l j . (11) J. Reilly and W. J. Ilichintxittoin, J . C / w ~ t z . So kz, so if we wait long enough tions to pseudo-first order and obtain the rate con- ( i . e . , until substantially all diamine molecules have stants from the corresponding equations in a been once-quaternized; x,'2b 3 0.5), the first term on the right of (21) becomes negligible compared to fairly direct way. In comparing diamines with the corresponding the second, and a plot of F,' ( x ) = In [1 - (x'2b)I mono-amine, a stoichiometric factor of two ap- against time gives a first approximation to k z . pears because one mole of diaminc naturally con- This value, together with the first approximation to tains two equivalents of quateriiiLnble nitrogen. kl from the previous case allows us to compute the If we designate by k1 the rate constant for the bi- correction term in (2l;jj and then a plot of molecular reaction between a mono-amine and an F2is>= In 11 -. .~.,'2b--- [!hl - k s ) / ( 2 k l - k,) 1 exp( - 2 k i 4 I alkyl halide, i t is numerically the Same in units against time gives a second approxirnation to kz. (1. 'mole min.) or (l./equiv. min.) \Then a diTABLE I1 amine is considered, the kl' of the above equation then becomes 2kl n here kI is the rate constant for ~ U d 4 T E R S I Z A T I O SO F nlIl.4SIC . h I I S B S 1/c:. b
