Sept., 1934
DISSOCIATION CONSTANTS OF ORGANIC BORICACIDS
Another feature of the observed values is reproduced by the calculated: the decrease of d In A/dT with increasing concentration at a given temperature. At very low concentrations, where the curves are parallel, with a slope of minus '/zon a log h-log t plot, the temperature coefficient is independent of concentration. But when the curves begin to flatten out toward the minimum, a decrease of the coefficient with increasing concentration appears. This is due to the shift of the minimum toward higher concentrations with increasing temperature, owing to increased dissociation of triple ions. The average differences between the observed temperature coefficients at 10-8 N and at 5 X 10-4 and 2 X lO-'N are, respectively, 0.10 and 0.25%, while the calculated differences are 0.11 and 0.23% at 325" Abs. and 0.12 and 0.25% at 300". Using the average values of the parameters a and a3 for tetra-n-butylammonium nitrate in anisole, together with various equations presented above, the conductance as a function of temperature may be calculated. The conductance minimum represents a characteristic point of the conductance curve; the influence of temperature on the location of the minimum is illustrated in Fig. 5, where Curve I is the calculated curve for the logarithm of the minimum equivalent con-
[CONTRIBUTION FROM
TEE
1865
ductance plotted against temperature and Curve I1 is the calculated curve for the logarithm of the corresponding concentration. The circles represent experimental values read directly from the curves of Fig. 2. Considering the simplicity of the assumed mechanism and the numerous assumptions and approximations made, not to mention possible experimental errors, the agreement between calculated and experimental values is quite as good as was to have been expected. For a temperature change of 128", Amin. varies approximately in the ratio 1:20 and cmin. in the ratio 1-2; maximum deviations in Amin. a t the extreme temperatures amount to about 20% and maximum variations in cdn. to about 10%.
Summary 1. The conductance of tetra-n-butylammonium nitrate and picrate in anisole, over the concentration range 0.00001 to 0.01 N and the temperature range -33 to +95.1", are presented. 2. The experimental results at concentrations up to about 0.001 N are in numerical agreement with results calculated from previously derived equations which are based on the hypothesis of ion association. PROVIDENCE, R. I.
RECEIVED MAY16, 1934
CHEMICAL LABORATORY OF THE UNIVERSITY OF CALIFORNIA]
Dissociation Constants of Organic Boric Acids BY BERNARDBETTMAN, G. 13. K. BRANCH AND DAVID L. YABROFF In two previous papers' we reported the dissociation constants of the phenetyl, the chlorophenyl and some of the hydrocarbon boric acids. A discussion of the relative strengths of these acids based on resonance and negativity was given. The present paper is a continuation of this work and deals with the dissociation constants of some other substituted boric acids, all derived from phenylboric acid. With the exception of onitrophenylboric acid, all the results are in accord with the principles we have discussed in the previous articles. o-Nitrophenylboric acid is anomalously weak. The dissociation constants were again obtained by measuring the PH of a series of paitially neu(1) (a) Branch, Yabroff and Bettman. THISJOURNAL, 66, 937 (1934); (b) Yabroff, Branch and Bettman, ibid., 66, 1860 (193.0.
tralized solutions with a hydrogen electrode. The constants we are using as a measure of acidic strength are actually a combination of activities and molalities, i. e., Ka = (")act. (A-) mol./ (HA) mol. We are again assuming that the measured PH is equal to the negative logarithm of the hydrogen-ion activity in the alcohol solutions, as well as in aqueous solution. The constants were again calculated by means of the eauation (H+)sct. (Na+ H+ - Kw/H+), Ka = M - (Na+ + H+ - Km/H+) M represents the total molality of the boric acid in the form of both acid and salt. Kw was again taken as 5 X for 25% alcohol (Nalc. = 0.0910) and as 1.5 X for 50% alcohol (NBIc.= 0.225). No other corrections were used
+
1866
BERNARD BETTMAN, G. E. K. BRANCHAND DAVIDL. YABROFF
Vol. 56
Isomer Ortho Meta Para except in the case of the second dissociation conB, % (direct titr.)la 6.45 6.47 6.46 stants of the carboxyphenylboric acids. There it B, % calcd. 6.48 6.48 6.48 279-281 309 was necessary to extrapolate to infinite dilution. M . p., O C . corr. (in- 101, resolidifies t o stant immersion) melt at 145-147 (dec.) The method is described later. M. p., "C.,of S. and J. 143.5-147.7 (anhy275-276.6 305.5 in preheated bath dride) (dec.) Rapid reduction of the nitrophenylboric acids occurred with the hydrogen electrode, so these m- and p-Carboxyphenylboric Acids.-These were prewere measured with a glass electrode. The disso- pared in 90 and 80% yields, respectively, by the oxidation ciation constants obtained for the nitro acids are of m- and p-tolylboric acids according to the method of probably less accurate than the others that we M i ~ h a e l i s . ~The meta isomer was purified by recrystallizahave measured since only one measurement was tion from water, from which it separates in the form of fine needles, m. p. 253' (corr.). Koenig and Scharmmade on each acid. The order of strength of beck4 report the melting point as 240'. The para isomer these isomers, however, is undoubtedly correct was recrystallized from water, from which it separates as since it was checked with indicators and found to fine needles melting a t 240' (corr.). The melting point be the same its that obtained from the glass elec- has been reported3n4as 225'. Attempts to obtain the ortho isomer by the oxidation of o-tolylboric acid were trode. unsuc~essful.~ A summary of the new constants obtained is m- and p-Fluorophenylboric Acids.-These were both given in Table I. prepared by the interaction of the corresponding fluoro-
TABLE I DISSOCIATION CONSTANTS OF ORGANIC BORICACIDSAT 25' Acid, boric
m-Fluorophenylm-Chloropheny Im-Bromophenyl-
Solvent
25% EtOH 25% EtOH 25% EtOH
Ka
1. io
x
10-9
1.35 1.46
3.66 X 10-lo 6.30 7.26 0.56 X o-Nitrophenyl25% EtOH 6.9 m-Nitrophenyi25% EtOH 9.8 p-Nitrophenyl25% EtOH m-Carbo xyphenyl- 25% EtOH (1st Ku) 2.22 X 10-5 p-Carboxyphenyl- 25% EtOH (1st Ku) 3.06 2.29 Benzoic wid 25% EtOH m-Carboxyphenyl- 25% EtOH (2d Ka) 1.12 x 10-10 p-Carbox yphenyl 25% EtOH (2d Ku) 1.90 1.971a 25Yo EtOH Phenyl0.463 X 10-1' p-Phenetyl50% EtOH 1.16 p-Phenox yphen yl- 50% EtOH 1.641b 50% EtOH Phenyl-
p-Fluorophenylp-Chlorophenyl$-Bromophenyl-
25% EtOH 25% EtOH 25% EtOH
Experimental Nitrophenylboric Acids.-These were prepared by the two nitration methods of Seaman and Johnson.2 The acetic anhydride method for the ortho and para isomers gave an average yield of 0.9 g. of the para compound and 10 g. of the ortho compound from 10 g. of phenylboric acid. These averages are from ten such nitrations. Seaman and Johnson report 0.3 g. of the para isomer and 8 g. of the ortho isomer from 10 g. of phenylboric acid. Our increased yield may be due to the fact that we used samples of highly purified phenylboric acid for the nitrations. The other nitration method for the meta isomer gave about the same yield as previously reported. The ortho and meta isomers were purified by recrystallization from benzene and from water. The para isomer was recrystallized from water. ( 2 ) Seanian and Johnson, THISJOURNAL, 63, 711 (1931).
phenylmagnesium bromide with n-butyl borate. m-Fluorobromobenzene was prepared by the thermal decomposition of m-bromobenzenediazonium fluoborate according to the method of Balz and Schiemann.6 p-Fluorobromobenzene was available commercially. m-Fluorophenylboric acid was recrystallized from benzene and from water. The para isomer was recrystallized from benzene. Both compounds separate as fine needles; m. p., meta 220221' (corr.), para 289-290' (corr.). AnuZysis.-B calcd., 7.74; B found (direct titration), meta 7.77; para 7.93. Neither compound has been reported previously. m- and pBromophenylboric Acids.-These were both prepared by the interaction of the corresponding bromophenylmagnesium bromide with n-butyl borate. mDibromobenzene was prepared from m-bromoaniline by means of the Sandmeyer reaction. m-Bromophenylboric acid was purified by recrystallization from benzene and from water. It crystallizes from the latter solvent in the form of fine crystals melting at 170' (corr.). +Bromophenylboric acid was recrystallized from 20% alcohol in the form of fine needles melting a t 312-315" (corr.) upon instant immersion. Bean and Johnson? report the melting point of the anhydride as 301-302* on the Maquenne block. AnaEysis.-B calcd., 5.21; B found (direct titration), meta 5.26; para 5.14. The meta isomer has not been reported previously. p-Phenoxyphenylboric acid was prepared by the interaction of p-phenoxyphenylrnagnesium bromide and nbutyl borate. In order to obtain a satisfactory yield of the Grignard reagent it was necessary to reflux the reaction mixture with the magnesium for about five hours. p Phenoxyphenylboric acid was recrystallized from benzene and from 25% alcohol. It crystallized from the latter solvent as short fine needles melting at 123-124' (corr.). Anulysis.-B calcd., 5.07; B found (direct titration), 5.05. This compound has not been reported previously. Miscellaneous.-Phenylboric acid, the three chloro(3) Michaelis, Ann., 316, 19 (1901). (4) Koenig and Scharmbeck, J . prakl. Ckem., [2] 128, 153 (1930). ( 5 ) Bettman and Branch, THISJOURNAL, 66, 1616 (1934). (6) Balz and Schiemann, Bey., 60, 1188 (1927). (7) Bean and Johnson, THISJOURNAL, 64,4416 (1932).
DISSOCIATION C!!NSTANTS
Sept., 1934
pheraylhic acids, an4 P-pheBetyl bale acid have been previously described.
OF GRGAWC BDRICACIDS
1867
I, We have usedlb Dericks a-factop for a-substituted acetic acids as a measure of negativity and this seems to confirm the above order. The dissociation constanks of the a-flmro, a-&ro, a-bromo and a-iodo acetic acids a t 25' are given by Scuddergas 2.17, 1.55, 1.38 and 0.71 X 1WS, respectively. The decreasing order of resonance
The experimental results are summarized in Table 11. Measurements were usually t a l a a t three concentrations, and a t each concentration the molal ratio of sodium hydroxide to the total acid was 0.4, 0.5 and 0.6.
TABLEI1 DISSOCIfiTION CONSTANTS AT 25' Acid
m-Fluorophenylboric m-Chlorophenylboric m-Bromophenylboric P-Fluor~~heny1b~jc g-Chlorophenylkoric p-Bromophenylboric o-Nitrophenylboric m-Witrophenylboric p-Nitrophenyl&ric m-Carboxypheqylboric #-Carboxyphenylboric Benzoic acid p-Phenetylboric p-Phenoxyphenylborie
Solvent, EtOH
26% 25% 25%
25% 25% 25% 25% 25% 25% 25% (1st &) 25% (1st KO) 25% 50% 50%
Molaiity raqge
Iletns.
9 9 9 8 9 9 1 1 1 12 8 11 9 9
0.06-0.02 .06- .02 .03- .01 .06- .02 .06- .02 .03- .01 .03 03
Ranex of
Ku
1.08-1.12 1.32-1.38 1.42-1.52 3.w-3.79 6.21-6.4 7.09-7.38
I
,03 03- .OD9 -02- ,005 .03- .005 .06- .02 .03- .01 I
2.15-2.30 3.00-3.11 2.20-2.36 4.56-4.78 1.13-1.18
Mean
Ka
1.10 X 1.35 X 1.46 x 3.66 x 6.30 X 7.26 X 5.6 x 6.9 x 9.8 X 2.22 x 3.06 X 2.29 x 4.63 X 1.16 X
1O-O 1010-9 10-10
10-10
10-10 10-lo 10-o lo-$ 104 10-6 10-5
lo-"
Av. dev. from
mean K5,%
1.1
1.0 1.8 2.3 1.2 0.9
1.7 0.7 1.8 0.9 .9
It was found that the second Ka of the carboxyphenylboric acids varied with concentrztt'ion. A value was obtained for infinite dilutioln by plotting P''~ against - l / d log Ku and fitting the resulting points to the theoretical Debye curve for activities.* There is a probable uncerti3inty of 10 to 20% in the extrapolation since the theoretical curve used was for aqueow wlutions. Three measurements were made a t each conceatration with the seccmd acjd group neutralized 40, 50 and SO%, reSpectively. The aversge of these three valves a t ea& concentration is given in Table I11 together with the rna8impm deviation.
interactions has been assumed to be I, Br, Cl and F. The experimental evidence for this order wrnes maialy from benzene substitution reactions,10but is not very definite: its existence bas beetl derived mainly from theoretical deductions. The iodo group is much larger than the other halogeno groups aad i t hbls bee0 assumed that its, valency electr~nswwld be more readily polarized than those of tbe smaller halogens. The fact that iodim, but not the other halogens, forms more than one bond to carbon in organic derivatives (iodinium compounds) has also been adduced as evidence for the resonance order. In an earlier the dissociation constants of the t h e e chlorophenylboric acids were reported. TABLE I11 m- AND P-CARBOXYPKENnBORICACIDSIN 25% ALCOHOL- It was assumed that resonance interactions of the chlorine atom were important in these derivatives SECOND Ka Met+ Para since the ortho isomer was of about the same Concn. Ka X 10' Concn. Kn X 1010 strength as the meta isomer. From the combina0 03 2.59 * 0.01 0.03 4 . 3 2 * 0.03 .02 2.38 .03 .02 4.00 .03 tion form, C 1 + o - ( O H ) 1 , it is seen that .01 2.14 * .03 .Ol 3.63 * .01 resonance WUtend to decrease tbe strength of .005 1.97 * .02 .005 3.37 * .03 the ortho and para acids. Negativity of cowse Extrapolated to Extrapolated to will increase the acidic strength in the order 1.12 x 1 0 - 1 0 1.90 x 10-10 ortho > m e b 7para, Discussion of Results If we assume the negativity order F 3C1 >Br Halogenopbenylboric Acids.-The decreasing > I and the old resonance order I >Br >C1 >F; (9) Scudder, "Conductivity and Ionization Constants of Organic order of negativity of the halogens is F, C1, Br, Compounds," Van Nostrand Co., New York, 1914,pp. 163, 99, 83, f
(8) Randall and Youpg, "Elementary Applications of Physical Chemistry," Chap. 28, pp. 7-8; book to be published.
189. (10)l e e , for example. Ingold, h a . trm. ahia., 48,797 (1929).
BERNARD BETTMAN, G. E. K. BRANCH AND DAVID L. YABROFF
1868
then the strength of the various halogeno phenylboric acids in a given position (0, m or $) must be F >C1 >Br >I. Actually the reverse order was found in both the para and meta positions. The experimental results obtained are of a comparative accuracy of about 5% since the three meta compounds were measured at the same time with the same electrode and the three para compounds were treated likewise. The new values for mand $-chlorophenylboric acids agree fairly well with those obtained before. It will be noted in Table I that the differences between the halogeno acids are greater in the para than in the meta position There is also a larger difference, in both the meta and para acids, between the fluoro and chloro acids than between the chloro and bromo acids. Orders of strengths other than the normal negativity order, F >C1 >Br >I, have been obtained previously in the benzoic acid series." This suggests some factor opposing the negativity effects in halogeno aromatic acids, but in the benzoic acids the differences in the strengths and the probable accuracy of the measurements are not such as to warrant any definite conclusions. In the halogenophenylboric acids the differences in the strengths seem to be definitely greater than the possible errors in the measurements. It seems reasonable to conclude that the assumed resonance order is in error and that the true order is F >C1 >Br. The fact that the meta acids show the same order as the para acids (although the differences are very small) is probably due to secondary resonance interactions between the halogen atom and the benzene ring. Nitrophenylboric Acids.-p-Nitrophenylboric acid is stronger than its meta isomer. The para nitro derivatives of benzoic acid, phenol and anilinium ion are all stronger acids than their meta derivatives. In a previous paper we have attributed this order of strengths to the resonance ~
~
N
O +I O .+ N ( Z I ) .
The latter
structure will tend to stabilize the acid-strengthening resonance in the case of a boric acid derivative, and the combination form of the ion largely responsible for the great strength of $-nitrophenylboric acid is -o)N+e-B(;: -0 (11) Kuhn and Wassermann, Hclv. Chim. Acta, 11, 3.31 (1928).
Vol. 56
o-Nitrophenylboric acid is weaker than m-nitrophenylboric acid, while in the other types of aromatic acids the ortho nitro compounds are stronger acids than their meta isomers. The negativity of the nitro group and its resonance interaction with the benzene ring would lead one to expect that o-nitrophenylboric acid should be considerably stronger than its meta isomer. It seems likely that ring formation has taken place /B(OH)B
giving rise to the structure
0,2
* This + form may be considered as either in equilibrium with the classical structure or as one of the forms whose combinations constitute the resonating molecule. In either case its existence tends to decrease the strength of the acid because of the negative charge imposed on the boron atom. The Referee of this paper suggests the possibility of hydrogen bond formation in o-nitrophenylboric acid as an alternative explanation of its weakness. In our method the molecule would then be repre-
.OH
.OH
ferred to ascribe the ring formation to a boron bond, as o-nitrobenzoic acid is not anomalously weak, but this evidence is not conclusive. Carboxyphenylboric Acids.-A comparison of the first dissociation constant of m-carboxyphenylboric acid with that of benzoic acid gives an approximate measure of the negativity of the B(0H)z group. In 25% alcohol the two acids have almost the same strength, Ka = 2.22 and 2.29 X respectively. From this it would appear that the B(0H)s group has nearly the same negativity as a hydrogen atom. However, B(OH)n
the resonance ([)cooi \
'0' ) -B(OHh . ,-
+
tends
COOH
to increase the strength of m-carboxyphenyfboric acid and the B(OH)z group should be rated as a slightly positive group, that is, the acid (H0)2B-CH&OOH should be slightly weaker than acetic acid. That the B(0H)z group is not markedly negative can best be attributed to a negative charge imposed on the boron atom by
DISSOCIATION C O N S T A N T S OF ORGANIC BORIC ACIDS
Sept., 1934
1869
interaction of its sextet with donor aioms. Whether this interaction is with the attached hydroxyl groups or with solvent molecules is not shown by the measurements. In p-carboxyphenylboric acid the resonance,
alcohol because of the insolubility of p-phenoxyphenylboric acid in 25% alcohol and water. m-Substituted Phenylboric and Benzoic Acids.-The expression ApK = loglo K H X H loglo KRXH in which RXH is the R derivative of the acid HXH, and K is a dissociation constant, has been used as a measure of the effect of the group, R, on the dissociation constant. ApK includes both negativity and resonance effects. Its magnitude and even its sign may vary with HXH. But it might be expected that the ApK values of a group tive charge nearer to the dissociating proton than are approximately the same when the acids are the resonance in the meta isomer. It is therefore meta derivatives of benzoic and phenylboric acids. not surprising to find that the para acid is stronger The classical structures of benzoic and phenylboric than either m-carboxyphenylboricacid or benzoic acids are very similar. The distances between the dissociating protons and the meta positions are acid. The second dissociation constant of m-carboxy- the same in the two acids. A meta group has phenylboric acid is less than that of phenylboric little or no resonance interaction with the acidic acid, just as the second Ka of isophthalic acid is group, and so only minor differences can arise less than that of benzoic acid. This agrees with from this type of interaction. Resonance bethe positivity of the carboxylate ion group. The tween the meta group and the benzene nucleus is second dissociation constant of p-carboxyphenyl- approximately the same in a benzoic acid as in boric acid is greater than that of the meta isomer. a phenylboric acid. However, this expectation This is in contrast with the phthalic acids, the is not borne out by the facts. This can be seen second dissociation constant of terephthalic acid by inspection of Table I V in which ApK is shown for some meta groups in both benzoic and being less than that of isophthalic acid. phenylboric acids. p-Phenoxyphenylboric Acid.-A comparison TABLE IV of the strengths of phenylboric, p-phenetylboric A$K VALUES" OF THE ?n-PHENYLBORIC ACIDAND THE mand p-phenoxyphenylboric acids is interesting. BENZOIC ACIDSERIES The last two acids are weaker than phenylboric APK APK. Phenylboric Benzoic acid. This may be attributed to the resonance Group acid series acid series
(E)*, 0j -B(OHL
'
which imposes a. negative
OR __.
+QR charge on the boron atom and so reduces the acidic strength. When R is a phenyl group this acid-weakening resonance is reduced because there is a competition for the unshared eleclrons of the oxygen atom between the group, -C!aHdB(OH)%and the phenyl group. Consequently the substitution of a phenyl for an ethyl groupincreases the strength of the acid to a much greater extent than could be due to the relative negativities of the groups when they are so distant from the dissociation proton. The dissociation constants in 50% alcohol are phenylboric acid, Ka = 1.64 X lo-"; p-phenoxyphenylboricacid, Ka = 1.16 X 10-l' and p-phenetylboric acid, Ka = 4.63 X 10-l2. The measurements were made in 50%
F
e1 Br OCaHs NO,
cooCHs
-0.75
-
-
.85
.87 .19 -1.55
+0.24
+ .15
-0.44
-
.45 .42 .14
.72
+ .36 + .07
The values of ApK for the benzoic and phenylboric acids are alike in that for both acids the order for the groups is nitro, halogeno, ethoxyl, methyl and carboxylate ion, and in that the first three are negative groups and the last two are positive. The magnitude of ApK for the group is larger, except for COO-, in the meta substituted (12) All of the phenylboric acid values are from measurements in 25% alcohol. The constants of the halogenobenzoic acids and the second dissociation constant of isophthalic acid are taken from Kuhn and Wassermann11 in 50% methyl alcohol and are referred to benzoic acid in the same solvent. The other values are from measurements in aqueous solution. The value for m-ethoxybenzoic acid is taken from Scudder, reference 9, p. 162; the other values are from Landolt and Barnstein, ed. 5, Vol. 11, pp. 1143, 1148. A p K for COO in the benzoic acid series has been corrected for the equivalence of the C O O - groups in the divalent ion by subtracting loglo 2.
H~WAR W. DSTA~~~WEXTHER
1870
Vol. 56
phenylbodc acid than i a &e c6despodding ktizoir aktiifional to'the h - m & repulsion 6f &e' profhi acid &ritratikk?. The! lafge ApK of groups in a negative group and e t i h ~ tIib s in&len& bwid acid d&va€W c ~ t aalso be ddn id a com- of th'e @oiip: It &by' bd ribtdd that Whig to the parison of the add stiragfh9 os bitt-yl, benzyl add above resonance the act&" of & tie@ive shbsfitu&$heri-yI&hyihk aCidS ~ 5 t hthose of the cofPe- ent is; laPgely on t h e bofoii' a t 6 d in a' boi'ic atid s p o ~ ~ g ~ s u b s t iaMmoniua t ~ e d ions. A$X for but on the hydroxyl grotifiin a benzaic acid derivabennryl mints butyl and for $phenylethyl mihhs tive, and so acts over a shorter distance in the bhi$1 are - 1.63 and -8.73 in the fkst s&es a d former than in the latter case. 1.27 and -0.78ib the second.la The n&ga€ivity We wish to express our appreciation to Mr. effects are &US a t least as @eat iin the b h t acids C. E. Larson of the Biochemistry Department who as in the ammwlium ions, th6dgh in the f&w carried out the glass electrode measurements on series the dissmiating protons are one atdm; f&- the nitrophenylboric acids. ther removed from the compared grbups~thariin SUMthe latter. We have c~osefithe above group9 fm The dissociation constants' O€ sorrie substituted this comparison because they have no resonah& phenqilboric add' deri:i3ativ$shave been' measured'. int;er&tibtl with the rest of the molkule. These have been discussed and compared on' the The above observations may k explained ba'sis'df negativity arid'resofiance. bv the theory of the baht add riesl)n&~ix, It is'pbintkd 6tlt &at' tlig old resofiance oraer (RB(OHh, R-B""')'. \OH' The strength of a boric asdtiaed' fof tHfe haloge'ns is wrotig' and tdat the tiW ofdkr i s F >C1: >BY. acid' depends on the interat&ibn of the uri&ar@d d-Nitr6phtnylboric acid; unlike other o-nitro electron pairs of a hydroxyl group with the sextet arij~zittc'aciiis;is weaker than its h e t a and para boron atom. This process impost?^ a negatk! isbtiiers. An efplanatiod for txis' has been' given: charge on the boron atom and is assisted bp tHe An eflhariced'efhct of tHe negativity' of substinegativity of the attached group. This effect is tuted gkoiips h'as l5een noted i n bbAd adil deriva(13) These values are calculated from dissociation constants given tives. by Yabroff Branch and Bettman, Reference Ib': and b$ HdI add
-
B ~ ~ R K E L ~CAL'IP. Y,
Sprinkle. THIS JOURNAL, 64, 3469 (1932).
[CONTKIStJTION
NO. 141 FROM THE EXPERIMENTAL STATION OF THE If. 1:
DU PONT DE
Ret!mvED'MA~'21, 1934
NEMOURS & COMPANY]
Polymerization under High Pressure BY HoWARD W.STARKWEATHER Since polymerization reactions involve greater hyde in greater detail. They showed that the contractions in volume tHan most resktions in rate of polymerization of isoprene was accelerated condensed) systems, it seemed reasonable to by, p&ro*ides,-Was retaMed by hydroquinbne, suppose that polymerizations would be more and followed:the'ri~tt!fbi a first order reaction. sensitive to pressure than most reactions. C o n a d aha. Petkrsdn4 contintied this investigsStrange and Bliss claimed' that the polymeri- titxi a i d c+xdi~lea!tHat pt+oiiiie catalyrit's were zation of b y h a r b o n s , such as butadiene, to ew5ntih1 tb;' the p6l~~ePikktib:n; atid that the rubber-like substances was greatly accelerated &ect of iiicie'ased p&sswe wgs only to.atkel&te when they were subjected to high pressure. the catalyzed, reacfih. Cyclotiexene oxide a s Bridgman and Conant2 reported the polymeri- poryniefized. vvitfi' great diffidulty. Tammsinri zation of isoprene, dimethyl-2,3-butadiene-l13,and' Pape' inve&iigated iri consid&rdk detail styrene, iridene, isobatyraldehpde and n-batyr- the polymerization of styr'e'ne, ibopretlk, vinyl aldehyde a t pressures up to 13,OOO atmospheres. aeetatir, dimetliylbutadierie arid indene at presConant' afid T0ngberg3inve&igated the polymeri- sures of 72d'to 3100 atmospheres and temperhzation of isoprene, vinyl acetate and n-butyralde- tures of 140 to 160". (1) Strange m d Blhs, British Patedl 3045 (1913) (2) J 3 r i & d and Conant, Prod. Nul. Aead Scr , 16, 680 (1929). (3) Conant aBd T-bhg, Tkr9 JowRNAL, 0% 1659 (1930).
(4) Conant and Peterson, i b i d . , 64, 628 (1932). (5) Tnhlmtlhn ahd Pape; 2.a$o?g. atZgCM. Chem..
Id,113 ( I Y 3 1 ) .
