1084
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table I11 s h o m t h a t moisture content exerts little effect on t h e slope of the lipide fluorescence 11s. palatability line but strongly affects the slope of the line relating salt fluorescence t o palatability. This evidence may be cited to exclude the glucoseprotein ieartion from responsibility for flavor change. The evidence, however, does not exclude the possibility t h a t the lipideamine reaction may contribute t o loss of palatability or t h a t it may be one of a chain of reactions resulting in flavor changes. DISCUSSION OF RESULTS
Objective methods of rating food products are t o be desired, in t h a t they offer rapid means of evaluation and are generally based on detvrminations t h a t can be made with more accuracy than most of the subjective determinations. On the other hand, objective detormiiiations have the weakness t h a t in most cases measurement of a single change may be inadequate t o determine quality. Further, the change may be related only incidrntally t o the changes responsible for quality deterioration. From the facts presented in this paper, it appears that' many factors may affect t h e salt-soluble fluorescence value of egg porvders. One of these is t h e moisture content of the poivder. M-ith high (4-5%) moisture content, t h e changes responsible for loss of palatability and those responsible for the production of saltsoluble fluorescing substances take place simultaneously and are closely correlated. Lndcr these conditions, for any one series of egg powders with similar processing history, the salt-wa,ter fluorescence value appears t o he a good index of palatability. However, when moisture contents are varied, the rate of development of each of ttic two factors is affected differently and the same correlation no longer holds. Below 2% moisture and with good quality egg pon.ders, sur11 i s are obtained by drying from the frozen state, t h e rate of development of salt-water fluorescing substances is lowered t o a greater extent than is the deterioration as measured by palatability. I n many cases the change in salt-water fluorescence value during storage is so slight t h a t it cannot be used to determine palatability. It also appears t h a t previous history of egg powder affects salt-soluble fluorescence value differently from its elfect on palatability score. Certainly the relation of the two values from one powder t o another may vary widely. The development of salt-water-soluble fluorescing substances is inci-
Vol. 38, No. 10
dental t o the development of off-flavor; thus the sources are not t h e same. Lipide fluorescence a s an index of palatability has several advantages over salt~-solublefluorescence. First, it measures deteriorative reaction of the phospholipides, which have been found t o be primarily responsible for flavor change (6). Sccond, the standard error of regression for lipide fluorescence is less than t h a t for salt-soluble fluorescence. Third, for low-moisture egg p o ~ ders lipide-fluorescence measurements have greater sensitivitlthan salt-fluorescence measurements, over t h e range of accept-. ability; t h a t is, lipide-fluorescence values for palatnbility sroi-e?. between 10 and 6 range from 2 to 35, as compared w i t h 19 to 25, for salt-fluorescence values. Although ether-soluble fluorescence has been found to parallel^ palatability scores better t,han salt-soluble fluorescence, it is possible t h a t development of fat-soluble fluorescing substances may also be incidental to the changes resulting in loss of p:datahility. I n any case, use of ether-soluble fluorescence as an index of pnlntability should be recommended only after a considcrablc volume of d a t a has accumulated on egg pon-ders of differing quality and history. ACKNOWLEDGMENT
T h e aut'hors are indebted to Marion Carter for assistnnce with calculations and t o Adele L. Dimick for determinations of saltwater fluorescence values. LITERATURE CITED (1) poggs. 51: (1946)
M.,and Fevold, H. L., ISD. E m . THEM.,38,
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(2) Dutton, H. J., and Edwards, B. G., Ihid., 37, 1123 (1918). (3) Ibid., I N D .ENG.CHEM.,A x a L . ED., 18, 38 (1946). (4) Edwards, B. G., and Dutton, H. J., IND.ENG.CHmr.. 37, 1121 (1945).
( 5 ) Ellinger, P.. and Holden, If., Biochem. J . , 38, 147 (1944). (6) Fevold, H. L.. Edwvnrds. B. G., Dimick, A. L., and Boggs, hl. M.,
ISD. ENG.CHEW.38, 1079 (1946). (7) Fryd. C. F. l f . , and Hanson, 9. W.F., J . SOC.Chem. I n d . , 64,55 (1946). ( 8 ) Olcott, H. S., and Dutton, H. J., ISD. ENG.CHEX.,37, 1119 (1945). (9) Pearce, 3. A , and Thistle, M. W., Can. J . Research, ZOD, 276 (1942). (10) Pearce, J. A., Thistle, XI. W., and Reid, M , , I b i d . , 21D,341 (1943).
Hydrogenation of Dinitriles in Liquid Methylamine B. S. BIGGS AND W. S. BISHOP Bell Telephone Laboratories, Murray H i l l , A'. J .
I
N T H E course of some
TI oik on polyamides it n as discovered t h a t the presence of alkyl substituents (preferably methyl groups) on some of the nitrogen atoms in polyamides exerts a desirable plasticizing effect on the product. I t thus became of interest to prepare S-methyl or AV,S'-dimethyl heiamethylene and decamethylene diamines. The preparation of S,S'-dimethyl diamines was accomplished by the reaction of the appropriate dibromides with a large excess of methylamine, b u t the process was too expensive for large scale use because of the difficulty of obtaining long-chain dibromides. Other general methods for the preparation of secondary amines (4,8, 11, 13) mere unsuitable for this purpose for one reason or another, so i t seemed worth while
to try the method of hydrogenating dinitriles in the presence of methylamine. Such a method \Tas used by Kindler (9) on mononitriles. [It was also used recently by Khitmore and co-workers (f2) to force the formation of a desired secondary amine.] As postulated by van Braun (3) and as discussed by Icindler and by Adkins (f), the mechanism of catalytic hydrogenation of a cyano group t o a n ,amine involves the intermediate formation of a n imine \Thich reacts with another molecule of hydrogen and is converted to a n amine. R-CN R-CH=NH
+ HP +R-CH=NH + H1+ R-CHI-XH,
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1946
Adiponitrile and sebaconitrile were hydrogenated in the presence of liquid methylamine with the formation of mixtures containing diprimary, primary-secondary, and disecondary diamines in the proportions of random distribution. The yield is faiored by high concentration of methylamine, and the degree of methylation can be controlled h y dilution of the methylamine with liquid gmmonia. The degree of methylation is determined by difference from a modified Van S1yke analysis for primary amino groups.
1085
factory method of controlling t,he per cent methylation is to use methylamine-ammonia mixtures and change the ratio of one to the other while the total number of moles of suppressor per niole of dinitrile is kept high enough (about 8 to 1) t,o assure a high yield of total diamines. In this way mixtures of diamines of any desired per cent methylation, up to about 5070, can be obtained in SO to 90% yield. Figure 3 presents data on hydrogcnations of adiponitrile and sebzconitrile in mixtures of methylamine and ammonia. CO3IPOSITIO.V OF PRODUCT
The product, obtained in this reaction consists of all t h e e of the theoretically possible compounds, H2S-(CI12)n-KII~, ,,---SHz, and CH,-N-(CII,) n-x’-CI13. CH,--S-(CH,) The imine, however, being highly reactive, combines with any primary aniine already present to form a complex which loses ammonia on further hydrogenation and gives rise to a secondary amine. II--C:H=SH
+ R--CHz--SH?
+P-CH-XH, I
II--CH?--S-H IL--CH--SH? R-CHz-XH
I
+ H2 --+
Ii-FHz
K-CH,-SH
+SH~
This side reaction was formerly a serious problem in the catalytic hydrogenation of nitriles to primary amines and cut the yields of the desired product to 50% or less of theory. It was especially troublesome when the nitrile being reduced was a dinitrile, for then the secondary amines produced were dipolymethylene triamines [I-IzS-(CHz) ,,-X-(CH2) .-HS], tripolymethylene
I
H tetramines l€IzX---(CH2) n--?;-(CHz)n-SH2],
I
etc.
This diffi-
H culty was overcome by du Pont (6) and by Schwoegler and Adkim ( I O ) by carrying out the hydrogenation in the presence of a large excess of ammonia. The latter, being present in larger proportion than the primary amine produced, presumably dominates the reaction of the imine, suppressing the undesired secondary amine and permitting a high yield of the desired primary amine. By this method yields of 80 to 90% or better of n-heptylamine, hexamethylene diamine, and decamethylene .diamine are easily obtained. By using methylamine as t>hesuppressor instead of ammonia, one would expect to take advantage of the reaction of imine with primary amine to force the formation of the desired methyiated diamines. This proved to be the case. The process is completely analogous to the preparation of primary diamines in the presence of ammonia, introduces no extra steps, and avoids the production of tertiary amines. CONTROL OF REACTIOSS
Although the yield of total diamines produced in the presence of methylamine is as high as when the hydrogenation is carried out in liquid ammonia, the yield of secondary amine groups a t the usual hydrogenation temperature is never greater than about 60% of the total amino groups; this indicates that almost half the imino radicals are hydrogenated directly without being influenced by the suppressor. This is in agreement with the fact that, when no suppressor is used, the yield of primary diamines is usually about 50%. It is advantageous to be able to prepare a diamine mixture of varying per cent methylation; i t was found that this can be done either by varying the amount of methylamine or by using a mixture of methylamine and ammonia. When the ratio of moles of methylamine to moles of dinitrile is low, the percentage methylation falls off (Figure 1) but the yield of diamines does also (Figure 2); consequently the more satis-
I
H
1
H These compounds were separated by fractional distillation because their boiling points are practically identical. The diprimary decamethylene diamine can be separated easily from the other two decamethylene diamines through the insolubility of i t a sebacic acid salt in ethyl alcohol, The other two compounds are much more alike in their solubilities but can be separated by patient recrystallization of their salts. Separation of the components is not necessary for determination of the composition of a mixture, since it was found that the reaction occurs in a purely random manner (6) and hence the mole per cent of diprimary, primary-secondary, and disecondary compounds in thc product are 100a2, 100(2ab), and 100b2,respectively, where a is the fraction of all amino groups which are primary and b is the fraction of all amino groups which are secondary. Evidence that the reaction is random consists of the fact that the same value for a was found by t x o independent methods of analysis ~ h i c involve h different components of the mixture, These methods are, first, the quantitative isolation of the sebacic acid salt of the diprimary compound, which furnishes a value for uz, and second, a modification of the Van Slyke method for amino nitrogen by which a value can be obtained for a, a term which includes the primary amino groups of the primary-secondary compound as well as those of the diprimary. Since the value of n obtained by the two methods is the same within the experimental error, it is known t h a t the reaction occurred in a random manner. Once this has been proved, the composition of any mixture can be determined by the modified Van Slyke analysis. TYPICAL HYDROGENATIONS
A two-liter hydrogenation bomb was charged with one mole (164 grams) of sebaconitrile (prepared by pyrolysis of sebacamide,
INDUSTRIAL AND ENGINEERING CHEMISTRY
1086
- __ -
-~~ -
C E C A M E Y Y L E N E SERIES
t WEXAMETYYLENE
-
50C!
1
k'iuiire 2 .
2
3
b
4 5 7 8 9 ;1 1'1 12 1'3 I 4 M C L S M E T H Y L A M N E PER M O L OF SEBACOhITRILE
15
16
l i e l d of Diamines as Affected by the imourit of 3Iethylaniine Used as Suppressor
e, 7 ) and 100 cc. of alcoholic auapension of Itaney nickel ,tqiiivalent t o about 10 grama of nickel) and was then placed in thc dryice box along vith a cylinder of methylamine. After a fen hours the bomb was removed from the box and 8 moles (248 grams) ~f liquid methylamine were introduced. I t is conrrnient to run the liquid methylaniinr directly into a tared Den.ar flask and Feigh it on a lahoratory balance in the hood. The bomb was 5ealed inimediarely while cold, hydrogen !vas introduced to tank pressure, and hydrogenation \vas carried out in the customary manner. The temperature was controlled a t 125"C. and. itt that cemperat,ure, the reaction was over in about 1 hour. Thc, iioiiih was cooled, and the product was rinsed out {vith alcohol, filtered free of catalyst, and distilled. It boiled at 142' C. at 12 mm. The product was a water-IT-hite liquid nhich on standing bocarrie mushy with n-hite crystals. ilnalysis by the modified Van Slyke method showed 7.497, primary amine nitrogen, which corresponds to 50.27, methylation. The yield wa8 162 grams, or 87% based on an average molecular w i g h t of 186. In similar experiments the following typical results ivc'rc, obtained: 164 grams (1 mole) of sebaconitrile in 480 grams (15.5 mole.5) methylamilie yielded 162 grams (877,) of diamine mixture which was 58'3 nicthyluted; 164 grams of sebaconitrile in 110 grams (3.55 moles) of methylamine yielded 136 grams (75.6 amine mixture which was 36% methylated; 164 grams nitrile in 68 gr~ims(1moles) of ammonia and 121 grams (1moles) of methylamine yielded 151 grams (56%) of a diamine misture which W:E 1 2 5 methylated; 216 grams (2 moles) of adiponitrile in 496 grams (16 moles) of mcthylaminc yielded 202 grams (78YG) of a product builing at 92" C. at 14 mm. The percentage methyl?h n was 47.8C,.
Vol. 38, No. 10
---_ ___
----
1
__
SERIES
--*
-
M O L PERCENT METH"LAM1NE IN TOTAL OF 0 MOLS OF AMMONIA A N D M E T H Y L A M I N E PER MOL OF SESACONITRILE OR A D I P O N I q q I L E
Figure 3 . Relation of Per Cent Methylation of Diamines t o 1IIethylaniiiie--immonia Ratio in the Suppressor
prwipitatioii iiiethud SIUCC thcir salts do not differ sufficiently in solubility. These mixtures are most conveniently analyzed by the modifid Van Slylte mc3thod. V A S SLYKE METHOD
One-gram samples of diamine mixture are dissolved in 5 7 , acetic acid and made up t o exactly 100 cc. \vith more of rhe acetic acid solution. aliquot portions of 10 cc. are used in the analysis, nhicli is run in the usual manner except that a shaking period of 15 minutes inst,ead of the usual 5 is allowed for the reaction witb nitrous acid. The method has been checked against pure hexamethylene diamine adipate and pure '-dimethyl hexamethylene diamine from hexamethj-lenc dibromide and methylamine. 0.1038 gram of hesamethylene diamine adipate gave 0.025 gram primary amine nitrogeu, or 24.08%. Theoretical is 24.147'. 0.500 gram of pure S,S'-dimethyl hexamethylene diamine gave 0.00022 gram priniary amine nitrogeii; this indicates that the compound is 99.777, methylated. I n calculating the per cent methylation from the per cent primary amine nitrogen, it must be remembered that the molecular weight of the compound is increasing as per cent methylation rises. For example, while the per cent primary amine nitrogen in an unniethylated decamethylene diamine is z"/172 X 100, that of a 50% methylated compound i3 l 4 / 1 S s X 100,and that of a 75% methylated compound is '/183 X 100, etc. If many samples are to be run i t is convenient to prepare a table or chart of values for ready reference.
R e d r s of other hydrogenations are indicated by the ctirvej;. LITERATURE CITED ISOLATlOh- O F DECAMETHlLENE DIA\IISE SALT O F SEBACIC ACID
A convenient sample-for example, 20 grams of a deciimethyl?ne dianiine mixture-is dissolved in 50 cc. of alcohol, and R hor aoncentrated alcohol solution of sebacic acid is added quickly unt,il the solution s h o w no alkalinity t o litmus. The salt solution is kept warm on a ?team bath, and almost immediately the white salt of the diprimary diamine begins to separate. After half a n hour the hot solution is filtered, washed with hot alcohol, dried on the filter and then over calcium chloride, and Tveighed. This separation is almost quantitative and may be used for an approsimate determination of the per cent methylation of a mixture. For analysis the salt may be conveniently crystallized from hot xater. It melts at 183" C. A sample of 0.349 gram yielded '1.0253gram of primary amine nitrogen, corresponding to 7.257,. Theoretical 73-as 7.50%. Hexamethylene diamine mixtures cannot be analyzed by the
(1) Adkins, Homer, "Reactions of Hydrogen", p. 53, University of Wisconsin Press, 1937. (2) Biggs, B. S., and Bishop, W. S., J . Am. Chem. Soc., 63, 944 (1941). (3) Braun, J. von, Blessing, G., and Zobel, F., Ber., 56, 1988 (1923). (4) Buck, J. S., and Baltzly, R., J . Am. Chem. Soc., 63, 1964 (1941). (5) Calingaert, George, and Beatty, H. 4.,Ibid., 61, 2751 (1939). (6) E. I. du Pont de Semours & Co., Brit. Patent 490,922 (May 16, 1937). (7) Greenewslt, C. H., and Rigby, G. W., U. 8 . Patent 2,132,849 (Oct. 11, 1938). (8) Henze, H. R., and Humphreys, D. D., J . Am. Chem. SOC.,64, 2878 (1942). (9) Kindler, Karl. and Hesse, Fritz, Arch. Pharm., 271, 439 (1933). (10) Schwoegler, E. J., and .Idkins, Homer, J . Am. Chem. Soc., 61, 3499 (1939). (11) Vanderbilt, B. h i . , U. S. Patent 2,219,879 (Oct. 29, 1940). (12) IThitmore, F. C., Mosher, H. S., Adarns, R. R., Taylor, R. B.,
Chopin, E. C., TTeisel, C., and Yanko, W., J . Am. Chem. Soc..
6 6 , 727 (1944). (13) Vinsns, C. F., U. S . Patent 2,217,630 (Oct. 8, 1940)
