NOTES
1956
observed molal heat capacities are shown in Table I-molal thermodynamic properties at integral temperatures in Table 11. The average deviation of the observed from the smoothed heat capacities was well under 0.1% except at temperatures below 20°K., where the small magnitudes impaired the accuracy. TABLEI1 MOLALTHERMODYNAMIC PROPERTIES OF POTASSIUM METAPHOSPHATE, KP08(c), CAL.DEG.-~ T,OK. 10 15 20 25 30 35 40 45 50
60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 273.16 298.16
CP
SQ
0.082 ,331 .748 1.370 2.128 2.947 3,784 4.600 5.383 6.809 8.043 9.143 10.12 10.98 11.80 12,57 13.28 13.97 14.62 15.23 15.81 16.37 16.90 17.40 17.88 18.35 18.81 19.26 19.68 20.08 20.48 20.87 21.25 21.63 20.60 21.56
0.018
,093 ,241 ,471 ,786 1.175 1.623 2.117 2,642 3.753 4,897 6,044 7.180 8.291 9.377 10.44 11.47 12.48 13.4i 14.43 15.37 16.29 17.19 18.07 18.93 19.77 20.60 21.41 22.20 22.98 23.75 24.50 25.24 25.97 23.98 25.83
H Q - HOD
0.144 1.114 3,727 8.943 17.65 30.32 47.15 68.13 93.10 154.2 228.6 314.7 411.1 516.7 630.6 752.5 881.8 1018 1161 1310 1466 1626 1793 1964 2141 2322 2508 2698 2893 3092 3294 3501 3712 3926 3359 3886
Vol. 64
INFRARED INTENSITY STUDIES OF A SERIES OF N,N-DISUBSTITUTED AMIDES BY C. D. SCHMULBACH~ AND RUSSELL S. DEAW W . A. Noyes Laboratory, Unrverstty of Illznozs, Urbana, Illanoas Received July 87,1960
The heats of formation of amide-iodine complexes for a series of amides of the type R’CON(R)zhave been determined in this Laboratory with the purpose of systematically studying the relative basic properties of amides.2 A search for additional criteria to be used in establishing the relative basicity of amides led to an investigation of the integrated intensity of the amide carbonyl band. In the past, considerable success has been achieved in arriving a t empirical or semi-empirical relationships between integrated intensities of a group vibration for a series of homologous compounds and a basicity or reactivity parameter indicated by u or u* values for substituent^.^ It is shown that in the N,Xdimethylamide series no such correlation exists. I t is further demonstrated that intensity cannot be used as a criterion for basicity in this series. A tentative explanation of the intensity data is proposed. Experimental Materials.-The preparation and purification of the amides and the purification of the solvent carbon tetrachloride have been described earlier . 4 Apparatus and Procedure.-The spectra of the amides were measured on a Perkin-Elmer Model 21 double-beam spectrometer fitted with a sodium chloride prism. The slit width was allowed to vary, in accordance with a fixed slit program, from the limits of 51 p a t 1735 cm.-l to 59 p a t 1600 cm.-’. The spectral slit widths, s, as computed from curves provided by Perkin-Elmer Corporation, varied only slightly from the value of 11 cm.-’. The wave length linearity in the carbonyl region was determined using water vapor spectra. The area under the carbonyl band, 50 cm.-’ to either ejde of the frequency a t maximum absorbance, was calculated by the application of Simpson’s rule using intervals of 2.5 cm.-’. At least four determinations were made on samples of each compound. The values for the apparent integrated intensities of the carbonyl band were calculated The concentration of amides wm corrected for volume expansion of the solvent a t elevated temperatures.5 Values for the intensity A were calculated according to the method of Wilson and Wells 6 Wing corrections were not applied The half-widths in cm.-’ are contained in Table I.
Results The entropy of KP03(c) at 298.16”K. is 25.83 The numerical results of intensity measurements e.u., with an estimated uncertainty interval of are given in Table I along with results reported’ on d~0.10e.u. On the assumption that the solid the primary amides. represents the ideal state, the heat content, As reported earlier,2 the addition of iodine to a HO Hao, at 298.16”K. is 3886 cal. mole-’. No carbon tetrachloride solution of an amide gives rise allowance was made for possible strain introduced to splitting of the carbonyl vibration frequency. by the repeated twinning. The calculations were The new peak which appears always at lower frebased on the simple formula weight for KPO,, quencies than the major band has been assigned to although Lamm3 suggested that the molecular an amide molecule which is bound to iodine through weight may be as high as lo* to 106. The cal(1) Eastman Kodsk Fellow. 1957-1958. culations were made on an IBM 704 computer (2) C. D. Schmulbach and Russell S. Drsgo, J . A m . Chrm. Soc.. 82, by a method that has been de~cribed.~ 4484 (1960). Acknowledgment.-J. R. L e k and A. W. Frazier (3) T. L. Brown, Chem. Reus., 68, 581 (1958I. (4) R . S. Drago and C. D. Schmulbach, THISJOURNAL,to be made the petrographic examination, J. P. Smith the X-ray examination and Inez Murphy the chem- published. (5) See “International Critical Tables,” Vol. 111, McGraw-Hill ical analyses. Book C o . , New York, N. Y., p. 28.
-
(31 0. Lamm. Arkiu Kemi, Mineral. Qeol., 178, No. 25, 27 (1944). (4) E P. Egan Jr.. and Z. T. Wakefield, THISJOURNAL, 66, 1953
(1 $461).
( 6 ) E. B Wilson, Jr., and A. J. Wells, J . Chem. Phys., 14, 578 (1946) (7) T. L. Brown, J . F. Regan, R. D. Schuetz and J. C. Sternberg, THIBJOUBNAL, 65, 1324 (1959).
Dec., 1960
1957
KOTES
DMF is not encountered in the primary amides (formamide and acetamide). This dserence can BAND OF A SERIES OF AMIDESMEASURED IN CARBON TETRA- be attributed to an internal steric interaction present in the N,N-dialkyl amides but not in the priCHLORIDE AT 30" mary amides. The amides may be considered as Xmax Avi/n, Amide A (om. cm. -1 resonance hybrids of limiting structures I and I1 TABLE I
INTEGRATED
INTENSITY
VALUEB"
FOR
THE
CARBONYL
-1)
N,K-Dimethylformamide D M F 5.78 1685 14 5 . 70b N,N-Dimethylacetamide DM.4 4.78 1662 23 S,N-Dimethylpropionamide DMP 4 . 2 2 1660 22 N,K-Dimethylbenzamide DMB 4.51 1644 19 N,N-Diethylacetamide DEA 3.90 1650 24 Formamidec 4.22 1709 15 Acetamidec 4 21 1678,1702 Propionamide" 3.85 1687 Benzamidec 4 . 0 6 1678 21 4 Values for integrated ictensities are in unite of 1 X 10-4 1. mol.-' cm.-z. Intensity value obtained a t 50". Data from reference 7, measured in chloroform.
I1 "La,
The rather sizable values of 22 and 19 kcal. calculated11,12for the free energy of activation necessary for reorientation around the C-N bond of DMF and DMA, respectively," emphasize the rigidity of the planar 0-C-N system. Both the intensity data and the entropy of formation of the the carbonyl oxygen. The integrated intensity DMA-I2 complex2 can be explained by assuming values for the complexed amide carbonyl bands that when R is a large group it undergoes steric interwere calculated by Method I described by Ram- action with the CHI group designated as one. I n say.8 Since the two bands overlap, and errors in the course of the normal vibration corresponding to the method introduce considerable inaccuracies of the adsorption a t 1662 cm.-l, the carbon-oxygen the order of 30%, the data are not reported. The bond lengthens and the C-N bond shortens.4 This intensities of these bands were always much larger causes the -CHI groups to interact and inhibits than those of the uncomplexed amide which had further lengthening of the carbon-oxygen bond. been calculated in the same fashion. The transfer The maximum value for the bond moment that may of electron density in the complex from the car- be attained is decreased for DMA and a correspondbonyl oxygen to the acceptor gives rise to increased ing decrease is observed in the intensity. This importance of the ionic form in the vibrational ex- effect is absent in DMF, so a larger intensity is cited state as compared to the ground state and also obtained than for DMA. This type of steric effect increases the length of the dipole in the ionic form, is also absent in the primary amides where a similar both resulting in larger values for integrated inten- intensity value is obtained for both formamide and sities. An increase in intensity also is reported to acetamide. It is informative to compare the integrated inoccur upon the addition of iodine to other solutions tensity of the amide carbonyl band with the basicity containing carbonyl compounds.9 of the amide toward iodine. Both the stretching of Discussion the carbon-oxygen bond and coordination to oxyThe intensity data (TabIe I) reveal several in- gen by iodine should be effected by electron donatteresting effects. In the primary amides (RCO- ing groups and a correlation might be expected? HE2),it has been found7that there is no correlation It has been demonstrated4 that the order of basicity between the carbonyl intensity and the inductive is approximately DMB = DMA = DMP > DMF. effect of the R substituent as measured by the sub- There is obviously no correlation in this series bestituent constant u*.lo tween the intensity data and the basicity of the A pronounced decrease in intensity is observed in amides. The greater inductive effect of the methyl propionamide compared to acetamide. It is pro- and ethyl substituents is shown clearly in the basicposed that rotational isomers exist in propionamide ity measurements. Two possible effects, either or both of which may and the presence in one isomer of a bulky group cis to the carbonyl lowers the intensity. An irregular be operative, will be proposed to explain the differences observed between the AH values and the integrated intensities. (1) Upon interaction with radiation, the DMA molecule does not have time to rearrange its methyl groups to relieve repulsions in the period of time band shape indicative of rotational isomers is ob- required to undergo a vibrational transition. Upon tained for propionamide.' The same effect is coordination to iodine such a rearrangement can indicated by our data for the intensity values for occur. A larger than expected entropy of formathe N,N-dialkyl substituted amides. The low tion of the complex indicates rearrangement does values obtained for DMP and DEA relative to the occur. (2) The steric interactions described above to value for DlMA are in part caused by this effect. The decrease in intensity of DMA relative to explain the intensity data are weak interactions. When a strong electron demand is made upon the ( 8 ) D. A. Rameay. J . A m . Chem. Soc.. 74, 7 2 (1952). (9) H. Yamada and K. Kosimrt, ibzd., 83, 1543 (1960). (IO) R. W. Taft, in "Steric Effects in Organic Chemiatry," M. S. Newman, Editor John Wiley and Sons, Ino.,New York, N. Y., 1956.
(11) H. S. Gutowsky and C . H. Holm, J . Chem. Phys., 26, 1228 (1956). (12) W. D. Phillips, %bid., PS, 1363 (1955).
NOTES
1958
Vol. 64
system, such as that involved in iodine coordination, pheric pressure and a t 1360 atm., and the volume these weak interactions have little effect on the AH change of activation in ml./mole. The rate oonvalue. These effects are slight compared to the stants were reproducible within 3% and the corenergies of bond formation, can be overcome in responding error in AV* is 0.5 ml. All volume part by rearrangement, and are manifested in the changes are very small in comparison t,o the molar entropy ~ h a n g e . ~ volumes, and it seems that racemization of these This study indicates that intensity values are compounds does not involve extensive desolvation. not reliable criteria for basicity when steric effects may be operative in the system under consideration TABLE I although sometimes they have been showna to Compd. Solvent T,OC. ka lip AV* parallel both basicity and reactivity in systems I DMF 114.8 0.0548 0.0553 - 0 . 2 free from steric interactions. .I66 -0.8 I1 DMF 50.8 ,159 Acknowledgment.-The authors gratefully ac.lo1 1.9 51.5 ,111 I1 EtOH knowledge the financial support given by the ReI1 EtOH-"*OH 51.5 .308 .288 2.0 search Corporation and the very helpful discussion I11 DMF 114.5 .I32 ,129 0.5 of the problem with Dr. T. L. Brown. Although the salt of I1 racemizes somewhat faster than the free acid the volume changes are T H E EFFECT OF PRESSURE ON T H E essentially equal. The carboxyl group evidently RESTRICTION OF ROTATION ABOUT does not contribute to the restriction of rotation. SINGLE BONDS Previous experiments have shown that the mesomeric effect of electron-withdrawing groups pura BY DONALD R. MCKELVEY AND K. R. BROWER to the nitrogen atom causes an increase in the Department of Chemistry, New Mezico Institdm of Mining und Techrate of racemization by stabilization of the planar nology, Campus Statran, Socorro. New Mezieo intermediate.s The same phenomenon should Receioed June 9'7, lS60 occur in t,he racemization of 11, but the resulting Detailed calculations of the geometry and strain polarization does not cause sufficient electrostricenergy of the transition states for the racemization tion of solvent to be reflected in the volume change of a number of optically active biphenyls' lead to of activation. the conclusion that the chief mode of deformation Experimental is bending of the single bonds which hold the interBromomesity1ene.-The method of Smith was used.' fering groups. Since very little stretching should Bromonitromesity1ene.-To a mixture of 14 ml. of acetic occur, there is no reason to expect that internal anhydride and 14 ml. of acetic acid was added 12 ml. of geometrical changes would produce a measurable white fuming nitric acid a t -15". The resulting solution increase in volume in the transition state. On the was added slowly to a mixture of 60 g. of bromomesitylene and 85 ml. of acetic anhydride while the temperature was other hand it is likely that a significant part of the maintained a t - 15' by addition of Dry Ice. The reaction restriction of rotation arises from solvation of the mixture was allowed to reach room temperature and was polar interfering groups. It recently has been re- poured into 300 ml. of water. The organic layer was ported that the rates of racemization of biphenyls diluted with ether, washed with 5% sodium hydroxide solution, dried, and distilled a t a pressure of 1 mm. The having ionic or polarized interfering groups are fraction boiling from 120-140' was collected and crystalstrongly dependent on the solvent and added lized from ethanol. The yield was 30 g. (41%), m.p. salts.2 If a considerable amount of electrostricted 51-53'; rec. m.p. 54". N-Benzenesulfonyl-N-carboxymethyl-3-bromomesidine .solvent is released during the activation process it bromonitromesitylene was reduced, benzenesulfonyshould be possible to detect a decrease in rate with The lated, and carboxymethylated by a sequence of steps increasing pressure. used in another ~ynt~hesis.5The yield was 17 g., m.p. This preliminary survey reports the volume 218-219'. Therec0rdedm.p. i~216.0-217.5".~ N-Benzenesulfonyl-N-carboxymethyl-l-amino-2-methylchange of activation for the racemization of d-Nprocedure of Adams and Sundstrom3 benzenesulfonyl-N - carboxymethyl - 3 - bromomesi- naphthalene.-The was used with modifications described in ref. 5. dine (I), d-N-benzenesulfonyl-N-carboxymethyl-1N-Benzenesulfonyl-N-carboxymethyl-l-amino-2,4-diamino-2,4-dimethyl-6-nitrobenzene(11) and d-N- methyl-6-nitrobenzene.-The procedure of Sdams and benzenesulfonyl - N carboxymethyl - 1 - amino 2- Gordon7 was used with modifications described in ref. 5. of Racemic Mixtures.-The cinchonine salts methylnaphthalene (111). The solvent used for of Resolution the acids were prepared by dissolving each acid together I and I11 was dimethylformamide, whereas I1 with the stoichiometric amount of cinchonine in approxiwas racemized in dimethylformamide, ethanol, and mately six parts of hot ethanol. The crystals which sepaethanol containing twice the amount of ammonium rated after several days of refrigeration were recrystallized ethanol, and the optically active acids were retrieved hydroxide required to neutralize the acid. The from by the methods described in the preceding references. volume change of activation was calculated from The d - N - benzenesulfonyl-N-carboxymethyl-3-bromomethe equation sitylene obtained in this way had [ a ] 2 6 ~ + 27.9' in DMF whereas the reported values is I ~ ] P ~ 4D 22.1". The other -RT ( 8 In k / 6 P ) ~= AV*
-
-
acids had rotations in agreement with the literature values.
in which k is the reaction rate constant. The results are shown in Table I which lists the conditions, the rate constants in hr.-l a t atmos(1) F. R. Waetheimer. J . Chem. Phys., 16, 252 (1947); K. E. Howlett, J . Chum. Soc., 1055 (1960). (2) J. E. Lefflsr and B. 11 Graybill, THISJOURNAL, 63, 1457, 1461 (1959).
(3) R. Adams and K. V. Y . Sundstrom. J . A m . Chern. Soc., 7 6 , 5474 ( 1954). (4) "Organic Syntheses," Coll. 1'01. New York, N. Y.,1950,p. 95.
11, John Wiley and Sons, Inc.,
(5) R. Adams and K. R. Brower, J . Ana. Chem. Sac., 78, 663 (195G). (6) R. Adams and M. J. Gortatoweki, ibid., 79, 5525 (1957). (7) R. Adams and J. R. Gordon. ibid., 78, 2458 (1950).
