NOTES
Nov., 1962
2277
figurationatl entropy of the chain, this behavior may THE RELATIVE BASICITIES OF ETHERS be predicted from the relative abilities of the ions BY HENRYE. WIRTHAND PAUL I. SLICK concerned to stretch the polymer chain. The lowest values of 'n then would represent the most highly Department of Chemistry, Syracuse University, Syracuse 10, New YorL stretched systems. This concept also may be used Received M a y d. 1988 to explain the variation of n values as the crossMeasurements of the basicities of cyclic imines linking agent is changed, with the lowest n values intoward trimethylboronl have shown that the basic dicating the greatest flexibility of cross-links. strength changes with ring size in the order: 4-> 5- > 6- > %membered rings. The same order TABLE I1 was observed using hydrogen bond2 and iodine APPARENT DISSOCIATIONCONSTANTSOF ACRYLICACID complex3a4formation. Studies of the dissociation :POLYMERS IN 1.0 M SALTSOLUTIOXS constants of ether-boron trifluoride complexes by Apparent pKa n manometric methods have shown that tetrahydroMole % (1 M salt) (1 M salt) furan is a stronger base than tetrahydr~pyran~ acrylate" Lit Na+ K+ L+ Na+ X+ and that the basic strengths of the acyclic ethers 98.4 4.43 4.73 4.90 1.4 1.7 1.8 92.4 4.50 4.93 5.10 1.4 1.7 1.85 decrease in the order: dimethyl ether > diethyl I n this work the ether > diisopropyl 75.8 5.47 5.80 6.08 1.85 2 . 0 2.1 relative basicities of some ethers and two alcohols a All crosai-linked with divinylbenzene (DVB). were obtained from a study of the equilibrium constants for the distribution of boron trifluoride beTABLE IJI tween two ethers in benzene solution. APPARENTDISSOCIATIONCONSTANTSOF ACRYLICA N D METHACRYLIC ACIDPOLYMERS IN 0.1 M SALTSOLUTIONS Mononier Acrylate 75.8 Mole 3'% 9 2 . 4 p,K. pK, Reaction n n H+-Li+ 5.70 1.5 6.70 1.7 H+-Na+ 5.75 6.75 2 . 0 1.8 H*-K+ 5.80 1.85 6.90 2 . 1 H+-Rb+ 5 . 8 5 1 . 8 5 7 . 0 0 2 . 1 5 H+-Cs+ 5 95 1.9 7.10 2.35
Methacrylate 93.6 77.8 pKa pKa n It 6.60 1.35 7.60 1 . 8 0.70 1 . 7 5 7 . 7 0 1 . 8 5 6.80 1.95 7.80 1.85 6.85 1.95 7.90 2.25 6.95 2.05 7.95 2.55
Experimental Procedure.-If a benzene solution of an ether (B1) is mixed with a benzene solution of either diethyl ether-boron trifluoride or dimethyl ether-boron trifluoride (Ba: BFa),the equilibrium
is established. The equilibrium constant may be determined from the equilibrium concentration of Bz: BFs and a knowledge of the original concentrations. The strong absorption due to the symmetrical B-F stretching frequency in TABLE IV EtzO:BFs a! 763 cm.-' or in MezO:BFa at 816 cm.-' wm used to obtain the concentration of the reference ether-boron APPARENTDISSOC~ATION OF ACRYLICAND METHA.CRYLIC trifluoride complex. Measurements on standard solutions ACIDPOLYMERS AT ZEROCROSS-LINKAGE showed that Beer's law was followed up to a concentration of Acrylic acid Methacrylic acid 0.1 M . 1.0M 0.1 M 1.0 M 0.1 M If a is the original molarity of Bz:BFa, b is the original ~Ka(rn-1) Salt Salt Salt Salt molarity of B1, c is the equilibrium molarity of Ba:BFa, and V is the ratio of the volume of Bz:BFJ taken to the total Li + 4.30 5.27 5.22 6.27 volume of mixture, then Na+ 4.65 5.30 5.34 6.37 aV = concn. of BS: BFa on mixing without reaction U+ 4.83 5.37 5.60 6.44 b( 1 V ) = concn. of B1 on mixing without reaction Rb + 5.40 6.50 ( a V e) = equilibrium concn. of Bz and Bt:BFa Cs + 5.52 6.58 b ( l - V) - (aV - e) = equilibrium concn. of B1 The equilibrium constant K is then
-
TABLE V APPARENTDISSOCIATIONCONSTANTSOF ACRYLICAND METHACRYL~IC ACIDPOLYMERS CORR~ECTED FOR EXTERNAL IONIC STRENGTH External ion, irMCCIQ
Li + Na + K+ concn. 0 . 1 M 1 . 0 M 0 . 1 M 1 . 0 M 0 . 1 M 1 . 0 M 0.792 0.781 0.778 0.658 0.769 0 . 6 0 5
9 3 . 6 Mole % MMA Apparent pK, Corrected p.K8
6.60 5.50
5.63 5.52
6.70 5.59
5.87 5.68
6.80 5.69
6.05 5.83
7 7 . 8 Mole % MMA Apparent pKB Corrected pKa
7.60 4.60
6.70 6.59
7.70 6.591
6.80 6.62
7.80 6.69
6.90 6.68
9 2 . 4 Mole % .AA Apparent PI
