Barker Hunter and Reynolds The Associating '872. The Associating Effect of the Hydrayen Atom. Part XIII. The N-€50 Bond. Esters of Curbamie Acid. LOUISHUNTER, By (MRs.) MINNIE BARKER and NORMANG. REYKOLDS. Measurements of the molecular weight of esters of carbamic acid reveal a high degree of molecular association in those esters possessing one or more unsubstituted imino-hydrogen atoms (I and 11),whereas those in which both hydrogen atoms are replaced (111)are non-associated. This as well as their tautomeric character is attributed to a hydrogen-bond (N-H-0) structure in the former. Further measurements indicate that esters of carbanilic acid (VIII)can suffer a diminution of molecular association by reason of the following three causes (a)co-ordination of the imino-hydrogen atom with suitable ortho-donor substituents (6) steric interference due to certain other ortho-substituents (c) steric interference due to the size of the alkyl group R.THEformation of hydrogen bonds by the arnido-group -NH*CO- has been the subject of previous parts o€ this series (J. 1937 1114; 1938 375 1034; 1939 484; 1940 332) and further indication of this tendency has been provided by X-ray investigation of acetamide (Senti and Harker J. Amw. Chem. SOC.,1940 62 2008) urea (Wyckoff and Corey Z. Kvzst. 1934 89 462) diketopigcrazine (Corey J. Amet.. Chma. SOC.,1938 60 1598) and polypeptides [19481 Efecj of the Hydvogefi Atom. Part XIII. 875 (Hughes and Moore ibid. 1942 64 2236) and by the infra-red spectroscopic study of proteins (Buswell Krebs and Rodebush J.Physical Chew. 1940 44 1126). It therefore seemed probable that esters of carbamic acid in which this grouping is present (I and 11)would possess NHR*CO,R' NRR'*CO,R' (11.1 (111.) a hydrogen-bond structure. Indication of hydrogen-bond association in these compounds is provided in their boiling points (see Table) those of the esters possessing one or more hydrogen B. p. B. p. NH,-CO,Me .................................. 177" NH,*CO,Et ................................. 184" NHMeC0,Me .............................. 158 NHMe*CO,Et .............................. 170 NHEtC0,Me .............................. 165 NHEt.CO2Et .............................. 175 NMe,*CO,Me ................................. 131 NMe,-CO,Et ..............................147 NE t,.CO,Me ................................. 155 NEt,.CO,Et ................................. 169-172 NMe(OMe)CO,Et ........................ 155 NMe(OEt)CO,Et ........................ 167 atoms (as in I and 11)being higher than those of esters in which such atoms are completely replaced by simple alkyl or alkoxyl groups (111). In the present investigation this prediction has been fully confirmed. The molecular condition of the esters of carbamic acid has been examined cryoscopically in benzene and in naphthalene solution over a range of concentration. As in previous parts of this series molecular association is inferred from molecular-weight measurements in all cases in which the factor of association (a) increases substantially with rising concentration ; ie.a steep association- concentration curve is taken to indicate molecular association whereas a flat or gently sloped curve (in the region CI = 1) is interpreted as indicating the absence of association. It is clear from the results (Fig. 1) that the esters fall sharply into two classes ; those possessing at least one unsubstituted imino-hydrogen atom (as in I and 11)are highly associated whereas those in which both imino-hydrogen atoms have been replaced (as in 11)are substantially unimolecular. This subdivision is in harmony with the tautomeric behaviour manifested by the former type but absent in the latter and it seems clear that carbamates such as (I)and (11)owe their molecular association no less than their tautomerism to molecular union through hydrogen bonds (N-H-0) the imino-hydrogen atom of one molecule being shared with the carbonyl-oxygen atom of a second as in the amides and sulphonamides (Chaplin and Hunter J.1937 1114). Such derivatives of carbamic acid therefore provide a further example of mesohydric tautonierism CB R*NH*CO*OH R*NH*C(:OH)-OR I ,1 I 1 I [R.N$:C(OH)a 0 R] (Hiintcr J . 1945 806). A chain polymer embodying these requirements and consisting of x +-2 molecules of the es ter (11)is depicted in (IV) where (a)and (b) are unperturbed states of the resonance hybrid. Multi-membered cyclic polymers of the type found in acetamide (Senti and Harker Zoc. cit.) involving no separation of charges are equally probable. That the imino-hydrogen atom of carbamic esters is responsible for their molecular association is confirmed not oiily by the fact that its replacement destroys association (Fig.l),but also that its engagement in chelate ring-formation with suitable donor ortho-substituents (NO, CO,R) 708 //vN\,Ill (pR 1 II ' NN\H I II NHPh*CO,R \OR (V.) ' (VI.) (VII.) (VIII.) UX.1 is similarly effective in suppressing molecular association. Thus in ethyl o-nitro- (V) and ethyl o-carbornethoxy-(VI) phenylcarbamate the preferential formation of intvanzolecdar N-H-0 Barker H.uut.ter altzd Reynolds The Associating bonds so reduces the tendency of the imino-hydrogen atom to form intermolecular bonds that the compounds are virtually unimolecular (Figs. 2 and 3). In the corresponding m-andp-isomers (e.g.VII) however the relevant groups are too remote to achieve chelation with the result that Effect of the Hydrogen Atom. Part XIII. the imino-hydrogen atoms are free to undertake intermolecular co-ordination and the compounds are therefore associated (Figs. 2 and 3). In this connexion the remarkably high degree of association exhibited in benzene solution by ethyl m-nitrophenylcarbamate (Fig. 2 curve 20) since it is even higher than that of ethyl phenylcarbamate (Fig. 1 curve 6) is probably due in part to a heterogeneous association (Hunter and Marriott J. 1940 166) between -NO and ZNH groups in adjacent molecules. The low solubility in benzene of the para-substituted carbanilates (VII) necessitated measurement of their molecular weights in naphthalene solution in which owing to increased thermal agitation of the solute molecules consequent on the higher melting point of the solvent lower factors of association are to be expected.This accounts for the relatively small slope of the curves for isopropyl P-nitrophenylcarbamate (Fig. 2 curve 21) ethyl p-nitrophenylcarbamate (Fig. 2 curve 22) and methyl and ethyl p-carbethoxyphenyl- carbamates (Fig. 3 curves 26 and 27) which are nevertheless interpreted as indicating strong association. A remarkable consequence of the fixation of the carbethoxyamino-group in (VI) in a position co-planar with the benzene nucleus is the protection thus afforded to the 6-position even in face of reactive substituting agents such as bromine.Treatment of (VI) with bromine yielded only ethyl 4-bro.w(ro-2-carbo~nethoxyphe~ylca~bamate which even with excess of bromine failed to brominate further. Nor could a dibromo-compound corresponding to (VI) be obtained by the action of ethyl chloroformate on methyl 2 4-dibromoanthranilate which failed to react under all conditions tried. Resistance to bromination has been recorded in similar circumstances for 3-nitroaceto-P-toluidide (Chaplin and Hunter J. 1938 377). A study of the carbanilates (VIII) and their derivatives has revealed that the capacity of the -NHCO,R group to cause molecular association is very sensitive to steric influences. For example the high degree of association of ethyl phenylcarbamate (VIII; R = Et) is very markedly reduced by the substitution of groups in the o-position (e.g.IX) as in ethyl o-tolyl- ethyl 2 :4-dimethylphenyl- ethyl o-chloro- and -2 :5-dichlorophenyl- ethyl o-brounophenyZ- and ethyl o-ethy2pheNyl-carbamates (Fig. 4 curves 34-39). Such groups can scarcely be considered to engage the imino-hydrogen atom in chelate ring-formation and it seems justifiable to assume that they play a mainly steric r61e. It would appear that the o-substituent A (IX) by virtue of its size not only orientates the group -NH*CO,R in such a way that the -CO,R group is remote from A but that the latter by its very bulk discourages the approach of a second molecule sufficiently closely to the imino-hydrogen atom to engage it in intermolecular N-H-0 bond-formation thus substantially reducing the proportion of associated molecules.On the other hand m- and p-isomers of (IX) (Fig. 4 curves 31-33) in which no such effects would be expected show a degree of association which is much higher and comparable with that of ethyl phenylcarbamate itself. Ortho-effects of this kind have previously been noted in numerous other instances ; e.g. Hewitt and Winmill (J. 1907 441) reported a similar tendency in the degree of association of liquid phenols measured by the Ramsay-Shields method. That hindrance of this kind is probably not the only factor controlling the degree of association in the above examples is indicated in Fig. 8 which compares ethyl phenylcarbamate with Methyl and ethyl cyclohexylcarbama2es. The reduced association of the latter (curves 53 and 64) as compared with the former (curve 52) can clearly not be ascribed to steric causes and is probably attributable to reduced acidity of the imino-hydrogen atom owing to the absence of a mesomeric effect in the latter.There are numerous other examples of the tendency to form hydrogen bonds being the stronger the more acidic the nature of the hydrogen atom concerned (see e.g. Hunter and Marriott J. 1941 777). Further effects attributable to steric causes are revealed by varying the group R in the carbanilates (VIII). Fig. 5 shows that the slope of the association-concentration curves of these esters in benzene solution undergoes progressive diminution with increasing size and complexity of the alkyl group (R); i.e. the molecular association diminishes in the order R = Me > Et > n-Pr > n-Bu > iso-Pr > iso-Bu (Curves 40-45 respectively).Inspection of the structural formula of these compounds will show that because of free rotation about the various single bonds the molecule can assume a great number of different configurations one being depicted in (X). It is evident that the larger the volume of the group R the greater will be its effect in hindering the approach of a second molecule towards the imino-hydrogen atom as a preliminary to hydrogen-bond formation. This explanation is in harmony with the above order from which it is evident that the branching of the alkyl chain as well as its length plays an important part in the sheltering effect of the alkyl group towards the imino-hydrogen atom.The series of carbanilates shown in Fig. 5 could not be pursued beyond the isobutyl compound because of the limited solubility in benzene of the succeeding homologues ; but a similar order Baykey Hwxtev and Reynolds The Associating of steric effect was found in the butyl carbanilates by measurements in naphthalene solution in which the compounds are more soluble owing to the higher melting point of the solvent. As v CH,Ph*NHCO,Et NHPh*CH,*CO,Et (X.1 (XI.) (XII.) would be expected from the above steric hypothesis tevt.-butyl carbanilate (Fig. 6 curve 48) has a lower degree of association than the isobutyl isomer (Fig. 6 curve 47) ; ethyl carbanilate (Fig. 6 curve 46) was measured in naphthalene for comparison. It is interesting though not unexpected that phenyl carbanilate (Fig.7 curve 49) is associated to about the same extent as ethyl carbanilate (Fig. 6 curve 46). These results are in close correspondence with those obtained from a study of the infra-red absorption spectra of the isomeric hexyl alcohols (Stanford and Gordy J. Amer. Chew. SOG.,1940 62 1247) in which the degree of association is found to diminish with increasing branching of the carbon chain in the neighbourhood of the hydroxyl group. The close connexion between hydrogen-bond association in the carbamic esters and their tautomeric character is strikingly illustrated by a comparison of ethyl benzylcarbamate (XI) with its isomer ethyl phenylaminoacetate (XII). In the latter the imino- and the carbonyl group are separated by a methylene-group and not only is (XII)devoid of tautomeric character but its molecular association (Fig.9) is very markedly reduced in comparison with (XI),in spite of the presence in its molecule of the associating groups imino-and carbonyl. This predisposition on the part of tautomeric hydrogen to engage in hydrogen-bond formation has frequently been reported in previous parts of this series [e.g. amides and imino-ethers (J. 1937 1114) pyrazoles and pyrazolines (J. 1941 3),thioacridone and thiodiphenylamine (J. 1942 640) cyanamides and aminoacetonitriles (J. 1945 SlS)] and provides a strong argument in favour of the theory of mesohydric tautomerism (J. 1945 806). EXPERIMENTAL. The following new compounds were prepared in the course of the investigation.Methyl diethylcarbamate colourless liquid with peppermint odour b. p. 15Al55' (Found N 10.8. C,H,,O,N requires N 10.7y0). Ethyl dicyclohexylcurbamate colourless viscous liquid with peppermint odour b. p. 304-306" (Found N 5.6. C15H2,02Nrequires N 5.5%). Methyl phenyl-n-butylcavbanzate deep yellow oily liquid b. p. 154'/21 mm. (Found N 6.6. C,,H,,O,N requires N 6.7%). Et~~ZphenyZ-n-bufylcarbamnate, deep yellow oil b. p. 156"/19 mm. (Found N 6.3. Cl,HI,O,N requires N 6.3%). Ethyl 4-chZoro-2- nitrophenylcarbamate obtained by prolonged boiling of 4-chloro-2-nitroaniline (2 mols.) and ethyl chloroformate (1 mol.) in carbon tetrachloride formed yellow needles from alcohol m. p. 99' (Found N 10.9. C,H,O,N,CI requires N 11.5%). Ethyl 3-nitro-p-toZyZcarbamute prepared similarly from 3-nitro-p-toluidine formed pale yellow needles from alcohol m.p. 56-57' (Found N 12.9. C,,H120,N, requires N 12.5%). Methyl p-carbethoxyphenylcarbamate white needles from aqueous alcohol m. p. 151-152" (Found N 6.2. C,,Hl,04N requires N 6.3%). Ethyl p-curbethoxyphenylcarbamute white needles from aqueous alcohol m. p. 129" (Found N 5.9. C1,H1,04N requires N 5.9%). Ethyl 4-bromo-2-carbomethox~~henyZc~rbama2e, white needles from alcohol m. p. 94" (Found N 4.6 ; Br 26.2. C1lH,,O,NBr requires N 4.6 ; Br 26.5%). Ethyl o-ethyl~henylcurbamute white platelets from aqueous FIG.1. Concn. M. a. Concn. M. a. 1. Ethyl /?-naphthylcarbamate (2 15). 4. Ethyl methylcarbamate (103). 2.90 262 1-22 2.86 126 1.22 4.40 290 1.35 4.80 137 1.33 6.16 322 1.50 6.73 149 1.45 7-93 354 1.65 10.38 173 1.68 12.26 184 1-79 2.Ethyl p-methoxyphenylcarbamate (195). 0.72 201 1.03 5. Ethyl p-chlorophenylcarbamate (200). 1.63 214 1.10 1-86 229 1-15 2-68 232 1.19 2.73 240 1.20 3.66 248 1.27 3.78 253 1.27 5-22 273 1.40 5.01 269 1.35 3. Ethyl p-bromophenylcarbamate (244). 6. Ethyl phenylcarbamate (165). 1.09 272 1.11 0.84 170 1-03 1.81 283 1.16 1.89 184 1.11 2.70 292 1.20 2-85 196 1.19 3.72 310 1.27 3.73 205 1-24 4.95 335 1.37 4.80 218 1.32 [1948] Efect of the Nydrogen Atom. Part XIII. FIG.1 (continued). Concn. M. a. Concn. M. a. 7. Ethyl a-naphthylcarbamate (215). 14. N-Carbethoxypiperidine (157). 1.04 216 1.00 2-29 154 0.98 1.43 226 1-05 3.41 153 0.98 1.61 228 1-06 4.64 152 0.97 3-03 253 1.18 6.11 153 0-98 3-45 268 1.20 8.2’7 152 0.97 8.Ethyl ethylcarbamate (117). 15. Ethyl phenylmethylcarbamate (179). 117 1.00 0.98 3-48 138 1-18 2.47 167 0.93 156 1.33 3-00 169 0.94 6.49 169 1-44 3-82 172 0-96 8.59 10.70 182 1.56 4.54 174 0.97 9. isoPropyl a-naphthylcarbamate (229). 16. Ethyl dicyclohexylcarbarnate (253). 0.45 232 1.01 1.16 245 0.97 1.57 244 1.06 2.01 245 0-97 2-85 259 1-13 3.18 242 0.95 4-13 269 1.17 4.58 237 0.94 4-81 270 1-18 5.30 236 0.93 i0. Ethyl p-ethoxyphenylcarbamate (209). \I 0.85 213 1.02 16a. Methyl phenyl-n-butylcarbamute (207). 1.22 216 1.04 (Coincident with Curve 16.) 1-72 227 1-09 1.05 201 0.97 2.21 199 0.96 11.Ethyl diphenylcarbamate (241). 3.05 196 0.95 1-30 235 0.98 3-67 196 0.95 2-31 234 0.97 4.68 195 0.94 3.53 236 0.98 4-81 237 0.98 5.94 240 0.99 17. Ethyl phenyl-n-butylcarbamate (221). 1.21 215 0.97 12. Ethyl diethylcarbamate (145). 2-14 213 0.96 1-74 144 0.99 3.35 208 0.94 2-88 144 0.99 4.21 207 0.94 5.21 142 0.98 4.99 205 0-93 8.18 143 0.99 9.22 143 0.99 18. N-Carbomethoxypiperidine (143). 13. Ethyl dimethylcarbamate (1 17) 0.93 133 0.93 1-66 115 0.98 2.71 132 0.92 2.83 113 0-96 4-27 132 0-92 5-16 113 0-96 5-25 130 0.91 5.91 114 0.97 6.55 115 0.98 19. Ethyl phenylethylcarbamate (193). 13a. Methyl diethylcarbainate (131).1.08 172 0.89 (Coincident with Curve 13.) 2-12 171 0.89 1.27 127 0.97 3-36 173 0.89 3.03 128 0.98 4.73 174 0.90 4.32 128 0.98 5.47 128 0.98 6-37 128 0.98 FIG.2. Concn. M. a. Concn. M. a. 20. Ethyl m-nitrophenylcarbamate (210). 23. Ethyl o-nitrophenylcarbamate (210). 1.66 236 1.12 1-92 210 1.00 2-32 253 1.21 3.01 214 1-02 3.48 289 1-38 4.38 217 1 ~04 5.01 344 1.64 7.38 387 1.84 24. Ethyl 4-chloro-2-nitrophenylcarbamate(246). 0.80 241 0.98 21. isoPropyl p-nitrophenylcarbamate (224) 2-52 246 1.00 1.12 242 1-08 3-76 250 1.02 3.27 267 1.19 5.01 256 1.05 3.97 273 1*22 25. Ethyl 3-nitro-p-tolylcarbamate (224). 22. Ethyl p-nitrophenylcarbamate (210). 1-82 220 0.98 1-58 228 1.08 2-49 224 1.00 3-80 249 1.18 4.03 230 1.03 6.00 269 1.28 5-15 232 1.04 8.22 29 1 1.38 5-85 233 1.04 3M 880 Barker HztNter aad Reyaolds The Associating FIG.3.Concn. M. a. Concn. M. a. 26. Methyl p-carbethoxyphenylcarbamate (223). 29. Methyl o-carbomethoxyphenylcarbamate 0.78 219 0?98 (209). 2.67 243 1.09 0.90 212 1.01 3.45 264 1.18 1.70 207 0.99 2.66 208 1.00 27.Ethyl p-carbethoxyphenylcarbamate(237). 3.51 208 1.00 0.69 229 0.97 4.77 215 1-03 1.87 249 1.05 3.28 265 1.12 30. Ethyl o-carbomethoxyphenylcarbamate (223). 4-26 275 1.16 5-26 285 1.20 1.77 221 0.99 2.80 222 1.00 28.Ethyl 4-brovno-2-carbomethoxy~henylcarbamate 3-61 223 1.00 4.41 224 1.00 (302) 0.92 294 0.97 5.34 225 1.01 1.73 295 0.98 2.58 302 1.00 3.37 309 1.02 4.10 312 1.03 FIG.4.Concn. M. a. Concn. M. a. 31.Methyl m-bromophenylcarbamate (230). 36.Ethyl o-ethylphenylcavbamate (193). 0.68 245 1.07 0.78 188 0-97 1.39 252 1.09 1.40 191 0.99 2.45 274 1.19 2.06 196 1.02 2.88 202 1.06 32.Ethyl p-chlorophenylcarbamate (see Curve 5). 37. Ethyl 2:5-dichlorophenylcarbamate (234). 33.Ethyl p-tolylcarbamate (179). 0.98 238 1-02 0.72 187 1.05 1.87 239 1-02 1.56 195 1.09 2.69 241 1.03 3.01 216 1-21 3.62 245 1-05 4-77 237 1.33 4.78 254 1.08 34. Ethyl 2:4-dimethylphenylcarbamate (193). 38. Ethyl o-bromophenylcarbamate (244). 0.99 0.95 241 1.82 201 1.04 2.60 246 1.01 2-50 206 1-07 3.25 248 1.02 3.35 211 1.09 4-26 248 1-02 4.50 219 1-14 5.42 251 1-03 35.Ethyl o-tolylcarbamate (179). 39. Ethyl o-chlorophenylcarbamate (200.). 1.12 177 0.99 0.52 181 0.91 1.59 181 1.01 2.00 183 0.92 2.08 186 1.04 3-79 188 0.94 3.04 191 1.07 4.66 190 0.95 3-69 195 1.09 5-20 190 0-95 FIG.5. Concn. M. a. Concn. M. a. 40.Methyl carbanilate (151). 43.n-Butyl carbanilate (193). 1-64 169 1-12 1.28 200 1.04 3.58 193 1.28 3.93 235 1.21 5-87 218 1.44 4.87 242 1.26 7-55 236 1.56 5.61 251 1.30 8.41 243 1.61 6.43 269 1.34 44.isoPropy1 carbanilate (179). 41.Ethyl carbanilate (165). 1.48 187 1.05 3.31 207 1.16 1.77 181 1.10 3.89 213 1.19 4-35 218 1.29 5.11 223 1.25 6.43 235 1.43 5-55 227 1-27 45.isoButy1 carbanilate (193). 42. n-Propyl carbanilate (179). 1.06 194 1.00 3.39 211 1.18 2-92 218 1.13 6-85 237 1.32 3.91 226 1.1.7 6-93 247 1.38 4-80 234 1.21 8.17 255 1.43 6-28 247 1.28 [1948] Effect of the Hydrogen Atom. Part XIII. FIG.6. FIG.7. Concn. M. a. Concn. .M. a. 1-80 176 4.11 190 5.23 196 47. isoButyl carbanilate (193). 46. Ethyl carbanilate (165). 1-47 202 2.96 215 3.83 218 4-79 222 5-69 228 1.06 1.15 1-19 1.04 1.11 1-13 1.15 1.18 49. Phenyl carbanilate (213). 1.24 218 2.37 229 4-15 245 5-66 256 50. o-Tolyl carbanilate (227). 1.15 231 2.99 249 4.39 261 5.12 265 5.85 2 72 1-02 1.08 1.15 1*20 1.02 1.10 1.15 1.17 1.19 48. tevt.-Butyl carbanilate (193). 1.07 1.95 1.01 51. cycloHexy1 carbanilate (219).2.68 200 1.04 1.39 223 1.02 3.96 206 1.07 3.24 237 1.08 4-70 240 1.10 5-08 246 1.12 FIG.8. FIG.9. Concn. M. a. Concn. M. a. 52 Ethyl phenylcarbamate (see Curve 6). 55. Ethyl benzylcarbamate (179). 53. Methyl cyclohexylcarbanzate (157). 1.59 198 1.11 2.84 213 1.19 1-17 160 1.02 4.79 230 1-29 2.04 168 1.07 5-93 241 1-35 2.98 177 1.13 7.19 253 1.41 3-97 186 1.18 5.26 194 1-24 56. Ethyl phenylaminoacetate (179). 54. Ethyl cyclohexylcarbainate (171). 1-33 177 0.99 2.54 185 1-03 1-22 179 1.05 4.94 193 1.08 2-65 191 1.12 5.64 194 1.08 3.7 1 197 1-15 6.51 107 1.10 5-49 205 1.20 6.44 212 1.24 56a. Ethyl o-tolylaminoacetate (193). (Coincident with Curve 56.) 1.70 105 1.01 2-62 199 1.03 3.81 203 1.05 5.39 208 1.08 7.40 213 1.10 alcohol m.p. 43-45' (Found N 7.4. CllH1502N requires N 7.3%). Ethyl 2 5-dzchlorofihenyl-carbarnate white needles from aqueous alcohol m. p. 54" (Found C1 30.3. C,H,O,NCl requires Cl 30.3%). Ethyl o-brorno~henylcarbamate,pale yellow liquid b. p. 153"/16 mm. (Found N 5.6. C,H,,O,NBr requires N 5.7%). Methyl cyclohexylcarbanzate white crystals from alcohol m. p. 75" (Found N 8.9. C,H,,O,N requires N 8.9%). Ethyl cyclohexylcarbamate white crystals from alcohol m. p. 55-56' (Found N 8.2. C,H1,02N requires N 8.2%). Revised melting points are recorded for the following ethyl p-chlorophenylcarbamate m. p. 70" (lit. 68O) ; ethyl p-methoxyphenylcarbamate m. p. 67" (lit. 63-64") ; ethyl 4-m-xylylcarbamate m.p. 61" (lit. 58") ; ethyl o-carbomethoxyphenylcarbamate,m. p. 67" (lit. 62"). Molecular-weight Data.-Molecular weights were measured cryoscopically the majority in benzene solution but those recorded in italics in naphthalene solution. In the tables concentrations are expressed as g.-mols. x 10-2/100 g. of solution the formula weights appearing in parenthesis; M is the apparent molecular weight deduced according to ideal-solution laws ; the association factor (a) is calculated as the ratio of M to the formula weight. The authors' thanks are due to the Chemical Society for a grant to one of them (N. G. R.). UNIVERSITY COLLEGE,LEICESTER. [Received,May 2nd. 1947.1