INDUSTRIAL AND ENGINEERING CHEMISTRY
472
propionate. Since all the methyl acetate reactions (Equations 3, 4, 5, and 7) are beneficial, the importance of using hrge proportions of this ester is clear. Inasmuch as the use of acetic acid with methyl acetate was not helpful (experiments 29 to 32), probably reaction 6 plays a minor role. Acetic acid would be actually detrimental if its presence caused reactions 3 and 7 to be reversed. LITERATURE CITED
Arnold, H. W., U. S. Patent 2,271,384 (Jan. 27, 1942). Bessi, S., and Angelo, B., Gam. chim. ital., 68, 215-24 (1938). Bezsi, S., Riccoboni, L., and Sullam, C., M m . acoad. Itatia, Classe sci. fis. n a t . nat.,8, 127-213 (1937). (4) Burkard, O., and Kahovec, L., Monatah., 71, 333-45 (1938). (5) Burns, R., Jones, D. T., and Ritchie, P. D., J.Chem. SOC.,1935,
(1) (2) (3)
400-6.
Chem. Forschungsgesellschaft m. b. h., Brit. Patent 469,976 (Aug. 6, 1937). (7) Claborn, H. V., and Smith, L. T., J . Am. Chem. SOC.,61,2727-8 (6)
(1939).
(8) Clough, G. W., J. Chem. SOC.,113, 526-54 (1918). (9) I. G. Farbenindustrie A.-G., Brit. Patent 360,822 (Oct. 30,1931). (10) Felten & Guilleaume Carlswerk A.-G. in Koln-Millheim, German (11) (12) (13) (14) (15)
Patent 375,639 (May 16, 1923). Filachione, E. M., Fein, M. L., Fisher, C. H., and Smith, L. T., Div. of Ind. Eng. Chem., A.C.S., Detroit, April, 1943. Fisher, C. H., Ratchford. W. P., and Smith, L. T., IND.ENQ. CHEM.,36, 229-34 (1944). Freudenberg, K., and Rhino, F., Ber., 57,1547-57 (1924). Godchot, M., and Vieles, P., Compt. rend., 202, 1358-60 (1936). Lecky, H. S., and Ewell, R. H., IND. ENG.CHEM.,ANAL.ED., 12, 544-7 (1940).
(16) (17)
Vol. 36, No. 5
Neher, H. T., IND. ENQ.CHEM.,28, 267-71 (1936). Patterson, T. S., and Forsyth, W. C., J . Chem. Soc., 103, 226871 (1913).
Patterson, T. S., and Lswson, A., Ibid., 1929, 2042-51. Powers, E. J., U. 9. Patent 1,927,295 (Sept. 19, 1933). Purdie, T., and Irvine, J. C., J. Chem. SOC.,75, 483-93 (1899). Ritchie, P. D., Jones, D. T., and Burns, R., U. S. Patent 2,183,357 (Dec. 12, 1939). (22) Ibid., 2,265,814 (Dec. 9, 1941). (23) Rohm, O., Ibid.. 1,121,134 (Dec. 15, 1914). (24) Rohm, O., and Bauer, W., German Patent 693,140 (June 6, (18) (19) (20) (21)
1940). (25) (26)
Schreiner, L., Ann., 197, 1-26 (1879). Smith, L. T., and Claborn, H. V., IND.ENQ.CEEM.,32, 6 9 2 4
(27)
Smith, L. T., and Claborn, H. V., IND.ENG. CHEM., N ~ W E ED., 17, 246, 370 (1939).
(1940). (28) Ibid., 17, 641 (1939). (29) Smith, L. T., Fisher, C. H., Ratchford, W. P., and Fein, M. L.. IND. ENQ.CHEM.,34, 473-9 (1842). (30) Starkweather, H. W., and Collins, A. M., U. 5. Patent 2,218.362 (Oct. 15, 1940). (31) Walker, J. W . , J. Chem. SOC.,67, 914-25 (1895). (32) Walker, J. W., Smiles, S., and Dover, M . V., J . Phya. Chem., 13. 574-84 (1909). (33) Watson, P. D., IND.ENG.CBEM.,32, 3 9 9 4 0 1 (1940). (34) Weisberg, 9. M., and Stimpson, E. G., U. 5. Patent 2,290,926 (July 28, 1942). (35) Wingfoot Corp., Brit. Patent 522,981 (July 2, 1940). (36) Wood, C. E., Such, J. E., and Scarf, F., J . Chem. Soc., 123, 6 D e 16 (1923). P ~ E E E N Tas E Opart of the Symposium on Lactio Acid and Derived Products before the Division of Industrial and Engineering Chemistry at the 106th Meeting of the AMERICAN CHSMICAL SOCIETY,Pittsburgh. Pa.
(Preparation of Methyl Acetoxypropionate)
PREPARATION FROM LACTIC ACID, ACETIC ACID, AND METHANOL E. M. FILACHIONE AND C. H. FISHER The conversion of lactic acid into methyl a-acetoxypropionate without the use of acetic anhydride, ketene; or acetyl chloride is described. Acetoxypropionic acid is formed satisfactorily when lactic acid, acetic acid, an entraining agent such as benzene, and an esterification catalyst such as sulfuric acid, are refluxed so that water is removed. Acetoxypropionic acid is transformed into its methyl ester by treatment with either methanol or
methyl acetate. The best means for esterifying acetoxypropionic acid consists in passing this acid and methanol vapor countercurrently through a packed tower maintained at 70' to 130' C. The manufacture of methyl aacetoxypropionate by this method would be particularly advantageous under wartime conditions as it would not require the construction of plants to convert acetic acid into acetic anhydride or ketene.
I
At least two approaches to the problem of preparing methyl acetoxypropionate with acetic acid as the acetylating agent can be followed. By the first, methyl lactate is prepared by esterification of lactic acid, and the methyl lactate is acetylated with acetic acid. The second approach comprises the acetylation of lactic acid with acetic acid, followed by esterification of the acetoxypropionic acid (11). Preliminary experiments showed that, although some of the desired diester (I) is obtained, methyl acetate is formed readily when methyl lactate is treated with acetic acid. Since this side reaction cannot occur when lactic acid is acetylated, the possibility of transforming lactic acid into methyl acetoxypropionate by the second route (Equations 2 and 3) was investigated:
N 1935 Burns, Jones, and Ritchie (3, 8) first demonstrated that methyl acrylate, a valuable synthetic rubber (9, IO, 13, 15) and resin (7) intermediate, can be made in high yields by the pyrolysis (6, 1.2) of methyl a-acetoxypropionate; it haq now become desirable to have efficient and low-cost methods
for preparing this diester from lactic acid. An attractive continuous method (4, which comprised the conversion of lactic acid into methyl lactate followed by acetylation with acetic anhydride or ketene, was described recently; but this method requires either acetic anhydride or ketene, which are more expensive than acetic acid. The use of acetic acid as the acetylating agent would have the advantages of lowering the cost of methyl acetoxypropionate (assuming comparable yields) and eliminating the need of plant facilities to convert acetic acid into acetic anhydride or ketene. The desirability of using acetic acid as the acetylating agent is increased by the fact that acetic acid as well as methyl acrylate is produced by the pyrolysis of methyl acetoxypropionate: CHsCOOCH(CH,)COOCHI 'Oo0 (1)
c;
CHsCOOH f CHs: CHCOOCHs (1)
CHsCOOH
+ HOCH(CH8)COOH --t
CH&OOCH(CH*)COOH (11) CH*COOCH(CHs)COOH CHIOH + (11) CH&OOCH(CH~)COOCHr (1)
+
+
H 2 0
(2)
+ Hg0
(35
INDUSTRIAL A N D ENGINEERING CHEMISTRY
May, 1944
TABLE I.
L
OF
ACETOXYPROt'fONIC ACID FROM ACETICAPIDR
Lactic Acid. Moles
Acetic Acid, Moles 8.75
AND
Ratio, Acetic: Lactio 8;58b
The acetyl derivative of lactic acid (11) has been prepared by Lhe reaction of lactic acid with acetic anhydride (2,11) and with acetyl chloride ( I , 6), but apparently no pretrious attempts to acetylate lactic acid s i t h acetic acid have been described. REACTION OF ACETIC ACID WITH LACTIC ACID
Since lactic acid has a carboxylic acid group as well as an alcohol group, at least two reactions can occur when a mixture of lactic acid and acetic acid is heated and the water of esterification is removed. h the desired reaction, the alcoholic hydroxyl group of lactic acid reacts with the acetic acid t o form acetoxypropionic acid, The alcoholic hydroxyl group also reacts with the lactic acid carboxyl group, forming lactyllactic acid (where x = 2) and similar linear condensation products (14) of lactic acid: HO(CH(CH,)COO]z H (111)
Probably the linear condensation products (111) of lactic acid react with acetic acid in two ways. The acetic acid may acetylate the terminal alcoholic hydroxyl group, or it may decreaEe the chain length of the linear condeneation products by acidolysis. Since all the reactions with acetic acid lead to the formation of acetoxypropionic acid, it would be expected that an excess of acetic acid would be helpful. Experience has borne out this expectation, A commercial, edible grade of 80% lactic acid, which was almost colorless, was used in most of the acetylation experiments. The lactic acid was acetylated by refluxing a mixture of lactic acid, acetic acid, an entraining agent such as benzene, and a small amount of an esterification catalyst such as sulfuric acid,
u1
I Fig.2. Reoction bet ween , I
25 IIACTIC"
Yield of Time of AcetoxyEntrainin Catalyst, Reflux, propionic Agent, Mf M1. Hr. Acid, % 5.9 55 Benaene 150 HzSOa, 1 1.0 147 71.5 6.6 Beneene: 200 Same 6 1.0 6.0 212 74 10. Same 16* 1.0 16.6 216 78.4 6.6 Same 16C 16.6 1.0 218 68 26.5 Benzene 300 2.6b 18.0 6.0 139 40 16.3 Ben%& 200 1.7b 8.0 4.0 314 14.5 55 Same Same 2.48 12.0 4.0 316 61 19.6 Same Same 3.3b 16.0 4.0 317 70 18.8 Same Same 4.16 20.0 4.0 319 67 12.8 Same Same 5.0) 24.0 4.0 321 77 21.0 Same Same 6.0) 4.0 28.0 323 14.3 71 Same Same 6.8b 32.0 4.0 826 61 Aame 11.0 Same 4.0 20.0 4.0 173 HiSOc 0.21 16.4 60 Same 15;4b 16.6 1.0 333 9.3 67 HaSOc: 1 Isopropyl 7 28.0 4.0 322 acetate, 200 scid waa 5 80% lactic acid solution wan wed except in expel:iment 147, in which 100% used b Correction made for amount of acetic acid removed with water by entraining agent. Approximate.
EyJ:
n
PREPARATION
Acrfoxypropionic Acid on Rufio of Acetic Acid to L o d i c Acid MOLE RATIO OF ACETIC ACID TO LACTIC ACID
1
473 I
ature and in presence of 2
IS
Sulfuric Acid) os shown by decrease in free ocidify
0 2-
*
OO
2
I TIME, HOURS
3
condensing the vapors, and returning the benzene layer to the reaction mixture (in a modified Dean and Stark tube), The reaction was considered complete when approximately one mole of water had been removed for eaoh mole of lactic acid in the reaction mixture. After the mineral acid had been neutralized with anhydrous sodium acetate (usually 4 grams of sodium acetate per ml. of sulfurio acid), the acetoxypropionic acid was distilled under reduced pressure. The results of the acetylation experiments show that acetoxypropionic acid can be made satisfactorily and in high yields by the reaction of acetic acid with lactic acid. The amount of lactic acid converted into acetoxypropionic acid varied with the amount of acetic acid used. The yield of acetoxypropionic acid was approximately 80% when a considerable excess of acetic acid was used (Table I). The dependence of yield upon the ratio of acetic acid to lactic acid is shown in Figure 1. The brown, viscous distillation residues, which probably consist mainly of acetylated condensation products of lactic acid, should be useful as a starting material in making monomeric lactic acid, methyl lactate, or acetoxypropionic acid. Since both acetic and lactic acids are inexpensive and potentially available in large quantities, acetoxypropionic acid could be made on a large scale at low cost. As ordinarily prepared, this acid is a moderately visrous fluid that supercools easily and is difficult to crystallize unless seeded. When crystallized, the scid is a low-melting solid (8). It distills at 75' C. (0.2 mm.), 90" (1 mm.), and 165' to 172' (75 mm.). REACTION OF ACETIC ACID WlTH POLY LACTlC ACID
Acetoxypropionic acid was prepared also by the acidolysis of polylactio acid (111) with acetic acid. The linear condensation polymer o€ lactic acid was prepared by dehydrating, under 20 mm. prwure, 200 grams of 100% lactic acid containing 2 grams of ptoluenesulfonic acid. Water was distilled from this mixture (ha1 temperature of reaction mixture, 150° C.) for several hours; the total distillate, mainly water, was 38.5 grams (approximately 96% dehydration). The distillation residue was then treated with lo00 grams of glacial acetic acid, and the resulting mixture was refluxed for 9.5 hours. After the addition of 8 grams of sodium acetate the mixture was distilled. The yield of acetoxypropionic acid was 26%. The results of this experiment indicate that the esterification of the alcoholic hydroxyl group is more rapid than the acidolysis of the ester group. REACTION OF ACETOXYPROPIONIC ACID WlTH METHYL ACETATE
Because of tbe high vapor pressure of methyl acetate, the reaction of methyl acetate with acetoxypropionic acid was studied in B closed system. A mixture of acetoxypropionic acid,
474
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 36, No. 5
lactate and methyl acetate. The yields, respectively, of methyl acetoxypropionate, methyl lactate, and methyl acetate were 34, 43, and 36% after 1 hour of refluxing, and 21, 52, and 48% Methyl Methyl Acetoxypropionate after 3 hours. I n both instances the combined yields of the Expt. YieLd, Tyw., Conversion. Acetate, lactic esters were more than 70%. Probably the distillation No. Molea C. %b % residues contained polylactic acid (111) or esters of polylnctic 1.25 100 214 2.5 100 219 acid, which should be of some value as a source of monomeric 223 2.5 125 120-130 225 lactic acid, methyl lactate, or acetoxypropionic acid. 2.5 226 2.5 140-150 Much higher yields were obtained when the esterification was 120-126 227 2.5 a 0.5 mole acetoxypropionic acid and 0.5 ml. concentrated H,SOd used: rarried out with methanol vapor in a packed tower under nonreaction period, 4 hours. equilibrium conditions. Slightly different techniques were used b Acetoxypropionic acid converted into methyl ester. Per cent of theoretical, based on acetoxypropionic acid destroyed. a t atmospheric and at 100 mm. pressure. d Bomb leaked during the experiment. Under a pressure of approximately 100 mm., a mixture of acetoxypropionic acid, methanol, and sulfuric acid was added dropwise into the top of a Pyrex tower (1 X 48 inches) packed methyl acetate, and a small amount of sulfuric acid was placed with */,-inch porcelain Berl saddles and was electrically heated. in the glass liner of a metal bomb and heated for 4 hours a t The temperature of the column was controlled and recorded different temperatures (Table 11). The contents of the bomb automatically. Methanol was passed into a heated vaporizing were then treated with enough sodium acetate to neutralize the flask, and the vapor issuing from this flask was passed into the sulfuric acid, and the products were iJolated by distillation under bottom of the packed tower. The methanol vapor was paseed reduced pressure. through the tower as long as acetoxypropionic acid was being The highest yield of methyl acetoxypropionate obtained by passed into the column and until the dry appearance of the the reaction of acetoxypropionic acid with methyl acetate was packing indicated that all the acetoxypropionic acid had reacted. 84% (Table 11). Acetic arid also was isolated. The most The vapors withdrawn from the top of the tower, which conextreme experimental conditions used (140" to 150" C. for 4 sisted of methanol, methyl acetoxypropionate, and other volatile hours) were not drastic. This reaction, which does not require products, were passed into the center of a steam-jacketed disarctic anhydride or ketene, could be employed to prepare methyl tillation column packed with small Berl saddles. The methanol acetoxypropionate. and water vapors that passed through this stripping still were ESTERIFICATION OF ACETOXYPROPIONIC ACID condensed. The products of higher boiling points, which were AND METHANOL collected at the bottom of the distilling column, were redistilled Because of the importance of the reaction, the esterification in a vacuum to determine the amounts of methyl lactate and methyl acetoxypropionate obtained. Yields of methyl acetof acetoxypropionic acid and methanol was studied extensively under various conditions. I n some of the experiments, mixtures oxypropionate as high as 72-75% were obtained at temperatures of,the two reactants were heated in the liquid phase and then of 80"-100° C. Methyl lactate also was produced (Table 111). When acetoxypropionic acid was esterified with methanol distilled t o determine the nature and amounts of the products. vapor in the packed tower under atmospheric pressure, the proI n other experiments the esterification was effected by passing cedure was slightly modified. As before, methanol vapor and methanol vapor and acetoxypropionic acid countercurrently acetoxypropionic acid were passed countercurrently through through a packed tower under atmospheric or reduced pressures. the tower, and the vapors withdrawn from the top of the tower The liquid-phase esterifications were carried out by refluxing were passed into the center of the steam-jacketed distilling a mixture of 0.5 mole of acetoxypropionic acid, 2.5 moles of column. The methanol distilling from the top of the column methanol, and 0.5 ml. of sulfuric acid. At the end of the reaction p a s condensed and returned through a liquid seal to the heated period the sulfuric acid was neutralized with sodium acetate vaporizing flask. When the esterification was carried out at (2 grams), and the products were isolated by distillation. The temperatures below 108' C., the material collected a t the bottom course of the reaction was followed by titration of small samples of the distilling column contained water and some methyl lactate of the reaction mixture to determine the free acidity. The and methyl acetoxypropionate, but most of the esters passed results (Figure 2) show that the free acidity almost reaches its downward through the esterification tower and were collected minimum value in 2 hours. High yields of methyl acetoxyin a flask at the base. The contents of the flasks located a t the propionate were not obtained because of the formation of methyl bottom of both the distillation and esterification columns were distilled under reduced pressure to determine the yields of methyl lactate and methyl TABLE111. METHYL LACTATE AND ACETOXYPROPIONATE PRODUCEDacetoxypropionate (Table 111). BY REACTION OF ACETOXYPROPIONIC ACID WITH METHANOLVAPORIN A When esterification was carried out in the packed PACKED TOWER tower under atmospheric pressure and a t temperaMethyl Methyl, AceAcetoxyLaotate. toxypropionate tures above approximately 108" C., the methanol propionic ConverConverExpt. Acid, HISO& Tzmz., Pressure, Time, sion, Yield, sion, Yield, vapor was recycled and passed through the tower No. Mole M1. Mm. Hr. %a %b %b until it appeared that all the acetoxypropionic acid 296 0.25 97-101 0.5 90-110 1.33 .. 22 .. 58 had reacted and passed as ester through the top of 297 95-102 90-110 0.10 1.2 10 72 0.5 .. .. 307 0.20 90-110 3.8 82-87 1 .o 75 .. 11 .. the tower into the distilling column. The material 78-95 308 0.20 93-98 1 .o 2.6 72 .. 17 .. 309 0.20 98-118 collected at the bottom of the column was then 95-130 2.1 72 1 .o . . 9 .. 0.20 115-122 70-110 1.3 310 1 .o 65 ..5 8 .. distilled to separate the products. 85-105 311 115-122 1 .o None 6.5 8 51 33 The data in Table I11 show that moderately high 295 0.5 0.25 122-135 Atm. 1.8 .. 47 .. 34 312 128-133 None yields of methyl acetoxypropionate were obtained by 3.0 Atm. 1 .o 24 62 15 39 313 128-136 1 .o 0.02 2.0 21 Atm. 25 55 46 the methanol vapor method, both under atmospheric 324 74-79 0.05 1 .o 0.5 Atm. 3 7 20 50 326 82-88 1 .o 0.05 0.7 Atm. 6 35 10 60 and reduced pressures. Most of the combined yields 327 Atm. 1 .o 0.05 ca. 95 0.6 6 11 28 54 328 0.05 101-108 1.0 Atm. 0.7 10 of methyl acetoxypropionate and methyl lactate 31 19 60 329 0.05 1.0 Atm. 74-79 14 2.5 7 35 71 ranged from 80 to 90%. The combined yields were a Per cent of acetoxypropionic acid converted. b Per cent of theoretical. on basis of ecetoxypropionic acid deatroyed. moderately high even in the absence of an esterification catalyst (experiments 311 and 312).
TABLE 11. METHYLACETOXYPROPIONATE FROM ACETOXYPROPIONIC ACIDA N D METHYLACETATE^
C
INDUSTRIAL AND ENGINEERING CHEMISTRY
May, 1944
DISCUSSION OF RESULTS
The production of methyl acetoxypropionate from lactic acid, acetic acid, and methanol by the methods described here have the advantage of not requiring the use of acetic anhydride or ketene, but the yields are not so high as those obtained by convereion of lactic acid into methyl lactate followed by acetylation with acetic anhydride, as described in the preceding paper. To. afford a comparison of the relative merits of the two methods, the materials costs of methyl scetoxypropionate prepared by the two methods were calculated. The prices assumed for the intermediate chemicals may not have been exactly correct, but the same prices were used for both methods and therefore the calculated material costs should be adequate for a preliminary comparison. I n making the calculations, the cost of sulfurio acid w e d a3 catalyst was not included, and i t was assumed that a n over-all yield of 85% acetoxypropionic acid could be obtained from lactic acid by treatment of the distillation residues with acetic acid. The other yields assumed in estimating relative costs w-ere: 75% methyl acetoxypropionate and 10% methyl lactate in the esterification of acetoxypropionic acid, 90% ðyl lactate in the esterification of lactic acid, and 96% methyl acetoxypropionate in the acetylation of methyl lactate. All yields were calculated on the basis of unrecovered starting materials. The calculated cost of materials indicated t h a t the acetoxypropionic acid method of making methyl acetoxypropionate is somewhat more expensive (approximately 2 cents per pound) than the previously described methyl lactate method (4). The aretoxypropionic acid method, however, has the advantage of not requiring plants for the manufacture of acetic anhydride or ketene. Owing t o the shortage of alloys and other construction materials, this advantage would be highly important under war-
475
time conditions if large quantities of methyl acrylate were manufactured by the pyrolysis of methyl acetoxypropionate. ACKNOWLEDGMENT
The assistance and cooperation of other members of the Carbohydrate Division of this laboratory are gratefully acknowledged. LITERATURE CITED
'
AnschUtz, R., and Bertram, W., Ber., 37,3971-4 (1904). Auger, M. V., Compt. rend., 140, 938 (1905). Burns, R., Jones, D. T., and Ritchie, P. D., J.,Chem. SOC.,1935, 400-6. Filachione, E. M., Fein, M. L., Fisher, C. H., and Smith, L. T., Div. Ind. Eng. Chem., A.C.S., Detroit, April, 1943. Fisher, C. H., Ratchford, W. P., and Smith, L. T.. IND.ENG. CHEM.,36, 229-34 (1944). Freudenberg, K., and Markert, L., Ber., 60B,2447-58 (1927). Neher, H. T., IND.ENQ.CHEM.,28, 267-71 (1936). Ritchie, P. D.,Jones, D. T., and Burns, R.,U. 8. Patent 2,265,814 (Dee. 9,1941). Rohm, 0.. Ibid., 1,121,134(Dec. 15,1914). Rohm, O.,and Bauer, W., German Patent 693,140 (June 6, 1940). Smith, L. T.. Fiaher, C. H., Filachione, E. M., Ratohford, W. P., and Fein, M. L.,Div. Org. Chem., A.C.S., Memphis, April 1942. Smith, L. T., FisheF: Cf H., Ratchford, W. P.. and Fein, M. L., IND.ENG.CHEM.,34, 473-9 (1942). Starkweather, H.W.,and Collins, A. M., U. 8. Patent 2,218,362 (Oot. 15, 1940). Watson, P.D..IND.ENG.CHEM.,32, 399-401 (1940). Wingfoot Gorp., Brit. Patent 622,981 (July 2, 1940). PRFJBENTED a8 part of the Symposium on Lactic Acid and Derived Productr before the Division of Industrial and Engineering Chemistry at the 106th Meeting of the AMFJRICAN CHFJMICAL SOCIETY, Pittsburgh, Pa.
CLASSIFICATION of TOBACCO Nicotine-Nornicotine Method C . V. BOWEN AND W. F. BARTHEL Bureau of Entomology and Plant Quarantine, s. Department of Agriculture, Beltsvil,e, Md.
HE recent discovery
Of the u.idespread OCcurrence of nornicotine in tobaccos (9) brings up the need for their rapid classification according to the predominant alkaloid. Markwood and Barthel (4) made such a classification based on the melting points of the picrate of the benzene-so1ub1e tobaccos giving picrate melting points above 215' C. were classified as nicotine type, those giving melting points between 175' and 200' C. as nornicotine type, and those between 190' and 215' C. as mixed type. No composition limits corresponding t o these melting point limits were given. Furthermore, i t is now known t h a t some tobaccos contain other benzene-soluble basic materials which influence the picrate melting point. The work has therefore been continued t o establish a rough correlation between composition and melting point for known mixtures of nicotine and nornicotine and t o check the classification scheme adopted against the melting points of picrates obtained from analyzed samples o f toharro.
T
*
The melting points of the picrates of known mixtures of nicotine and nornicotine indicate that the melting point of .the steam-volatile alkaloid picrate may be used as a means of classifying tobaccos as to alkaloidal type. According to the upper limit of the melting point spread, the tobacco is classified as nicotine type (melting point above 211' C.), mixed nicotine-nornicotine type (melting point 198-211 and nornicotine type (melting point below 198' C.). Six tobaccos of known nicotine and nornicotine content were tested for melting point of mixed picrates, and they were found to agree with the classification.
c.),
RELATION BETWEEN PICRATE MELTING POINT AND COMPOSITION
Known mixtures of standard nicotine and nornicotine solutions were treated with aqueous picric acid solution to obtain mixtures of the coprecipitated picrates. The standard solution of nicotine was prepared from a sample t h a t had been vacuum-distilled, treated with nitrous acid to remove any secondary amines, and then steam-distilled from a n aqueous alkaline solution. T h e nornicotine used in the standard solutions was identical with t h a t
