Preparation and Characteristics of Synthetic Constant-Yield Mixtures J. 0. BAXTER, E. LEB. GRAY, AND A. 0. TISCHER Eastman Kodek Company, Rochester, N. Y.
I
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N THE original experiments on molecular distillation conducted by Burch ( I ) , Washburn (6),and Waterman (?), each worker pointed out the difficulty of securing adequate drainage of the distillate from the relatively large condensing surface necessarily employed. The change in the degree of overlap in the drainage from one fraction to another is serious where the volume of the fractions varies considerably during distillation. Furthermore, in the present state of our knowledge it is not known how a change of rate in the distillation of one molecular species affects the rate of distillation of another species occurring in the same oil. Thus, where vitamin A is being distilled from fish oil, the potency of the distillate is dependent not only on the rate of distillation of the vitamin A but on the quantity of glycerides distilling a t the same time. With much diluent the potency is low; with little diluent the potency is high, and i t is not certain whether the variation in the quantity of diluent affects the intrinsic distillability of the vitamin. These considerations led Hickman (8) to adjust the composition of fish oils during analytical distillation so that the rate of distillation of the diluent remained constant during the whole distillation of the vitamins. Alternatively he addedvitamin concentrates to a constant-yield oil (C.Y. 0.) and performed distillations from the mixture to obtain the characteristic elimination curve of the vitamins. The use of this method has been described fully, and the present paper deals chiefly with the preparation and choice of materials for producing a constant-yield or a controlled-yield oil. For effective use such an oil should satisfy rather stringent conditions. It should distill over the range 100" to 260" C. in a continuous molecular still, yielding approximately the same
weight of distillate for each equal increment of temperature. It is a convenience if the distillates are liquid a t room temperature, and, in order that the oil be related as closely as possible to natural oil, it should consist of mixed glycerides but should contain neither cholesterol nor free fatty acids. A large selection of fatty acids was not required for the preparation of the desired glyceride mixture. A blend of acetic, butyric, the mixture of myristic and lauric acids from saponified coconut oil, and the highly unsaturated CIS acids from saponified perilla oil proved sufficient for the purpose. The coconut and perilla oils were saponified by the method of Marcus (6) in which 50 per cent aqueous potassium hydroxide is used. This procedure is excellent where large amounts of fat must be saponified.
Preparation of Constant- Yield Mixtures Glycerol is immiscible with the higher fatty acids, and it is necessary to employ some device for bringing the two liquid layers into contact during reaction. Long (4)achieved mixing by a modified Witt stirrer, revolving a t high velocity; the bulb was supplied with a vigorous stream of carbon dioxide or nitrogen. Hilditch (3) proposed phenol as a mutual solvent for glycerol and fatty acids. On a large scale both of these methods have disadvantages. The former requires too large a consumption of compressed gas, and the use of the latter makes it necessary to free the synthesized glycerides from inconveniently large amounts of phenol. The method finally adopted worked well and is worth discussing in detail:
A method has been devised for the preparation of pure triglycerides or mixtures of glycerides, which requires no catalyst and proceeds at temperatures substantially lower than the esterification procedures hitherto described. The method prevents almost completely the socalled bodying reactions that glycerides undergo when heated above 200' C. in air. Furthermore, the reaction is readily adaptable to operation on a large scale. The method has been applied to the preparation of a glyceride mixture, the so-called constant-yield oil, which boils in controlled quantities at temperatures ranging from 100' to 260' C. under molecular vacuum. This oil is suitable for the analytical distillation of a variety of compounds and mixtures of compounds whose elimination curves may be desired. It has found particular use in the analytical distillation of dyes and vitamins A and D in this laboratory. 1112
The charge of glycerol and fatty acids, weighing usually about 14 kg., was introduced into a 22-liter flask and heated for 4 hours a t 120" C. with vigorous stirring. A t the end of that time esterification had occurred to such an extent that complete miscibility was obtained. To the clear aolution 1500 cc. of chlorobenzene were then added. The flask was fitted with a stopper containing a thistle tube and a thermometer projecting below the level of the liquid. Through the sto per was also inserted a 12-inch (30.5-cm.y distilling column which was thoroughly lagged and connected to ti vertical Liebig condenser. This was so arranged that condensate was collected in a separatory funnel as shown in Figure 1. The c o n t e n t s of the flask were then heated until d i s t i l l a t i o n of the chlorobenzene occurred. The water evolved during esterification distilled over i n a binary chlorobenzene-water mixture, and separated out in the upper layer collected in the separatory funnel. The lower layer of chlorobenzene was returned from time t o time t o the distillation flask in sufficient amounts to keep the contents at 170" t o 175' C. The progress of the reaction was followed by measuring the volume of water collected. Data for a typical run made with glyceride m i x t u r e T-131 and no catalyst are as follows; the weight of the
1113
INDUSTRIAL AND ENGINEERING CHEMISTRY
OCTOBER, 1937
charge was 14,200 grams, and the preliminary heating lasted 4 hours at 120" C . : Time
Hours 0 1 2
3
Temp.
of Liquid O
C.
145 155 165 172
Water Removed Per cent of themy 0 15.1 32.0 42.2
Time
Temp. of Liquid
Hours 8 11 17
c. 173 175 175
Water Removed Per cent of theory 66.7 83.5 91.5
At the end of 17 hours the mixed glycerides had an acid value of 12.3. The free acid was removed by mixing the glyceride with half its volume of ethyl alcohol and neutralizing it to phenolphthalein with alcoholic potash. The mixture was then diluted with an equal volume of water, and the glycerides were extracted with ether. After removal of the ether and chlorobenzene, the residual glycerides were distilled in a cyclic molecular still.
Distillation Data Two glyceride mixtures (T-142 and T-146) covered the temperature range of 100" to 220' C. satisfactorily. Their fatty acid composition and distillation data are given in Table I. Equal weights of the fourteen fractions thus obtained were then mixed to prepare blend T-170 whose distillation data are recorded in Table 11. As a source of glycerides boiling from 220" to 260" C., it was convenient to use cod liver oil residue (that is, cod liver oil from which the low-boiling constituents, TABLE I. DATAON GLYCERIDE MIXTURES Initial and Fraction Distn. Weight of Final Rates No. Temp. Fraction of Distn. 0 c. Grams Drons/min.. Mixture 1 (T-142); Total Weight of Reactants = 14 200 Grams. Molecular Proportions,. Rut r.ic Acid 2.5 Coconut Acids' = 1.0 (Abid Value, 264.5). Perllla l c i d s = 1.5 (Add Value, 199.5), Glycerol = 2.3 630 180-120 80-100 540 180-120 100-120 720 180-120 120-140 180-120 2160 140-160 2160 180-120 160-180 1980 180-120 180-200 180-120 1170 200-220
_.
Mixture 2 (T-146). Total Weight of Reactants = 14 410 Grams; Molecular Proportions, B'utyric.Acid = 1.0, Acetic Acid = .O, Perilla Acids P 0.5 (Acid Value, 199.5), Glycerol = 1.0 1 80-100 1890 , 180-120 2 100-120 1350 180-120 180-120 3 120-140 4 140-160 405 180-120 1215 180-120 5 160-180 2250 180-120 6 180-200 1665 180-120 7 200-220
vitamins, and cholesterol had been removed by molecular distillation). In the distillation of blend T-170, the glyceride charge amounting to 10 kg. was distilled until only 3.5 kg. remained. Then 3.5 kg. of cod liver oil residue were added, and distillation was resumed until no more distillate could be collected at 260" C. I n this way twenty fractions were obtained distilling from 50" to 260" C., as noted in Table 11. The elimination curves of vitamins and dyes are best determined with a constant-yield oil distilling a t temperatures from 100" to 260" C . Trial showed that fractions 6 to 19 of T-170, when properly blended, distill sufficiently uniformly over this range of temperature. The pilot composition and distillation data of the blend, T-175, are given in Table 111; a temperature-yield curve is given in Figure 2. Precise directions for this blending cannot be included because the behavior of any such glyceride mixture varies somewhat, but the general method of procedure is described in the following paragraphs. A test sample was first prepared by mixing equal weights of fractions 6 to 19 of blend T-170. This sample was diluted
FIGURE 1. ARRANGEMENT OF APPARATUS
with an equal weight of cod liver oil residue1 and distilled, employing the technic developed by Hickman (2). The temperature-yield curve was similar to that shown in Figure 2, but the maxima and minima were more widely separated. T o flatten out this curve, the average weight of glyceride distilling over a 10" interval between 100" and 220' C. was calculated. The weights of each of the constituent fractions were then increased or decreased enough so that redistillation would yield closely this average weight. A marked improvement in uniformity resulted, and this blend T-175 (Figure 2) was used in a great number of experimental distillations. Obviously the leveling process could be repeated as often as necessary. A straight-line graph, the ideal condition, has not been realized as yet. Experience has shown, however, that the elimina1 The addition of high-boiling glycerides is necessary in order that the last stages of the distillation may be facilitated. The molecular still cannot be operated with a volume of liquid less than 30 00.
TABLE11. DISTILLATION OF BLEND T-170 Fraction
No.
Temp.
1 2 3 4 5 6 7 8 9 IO 11 12 13 14 15 16 17
50-60 60-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 180-190 190-200 200-210 210-220 220-230 230-240 240-250 250-260
C.
19 l8 20
Weight of Pressurea Fraction M n . X 108 Grams 10 234 5 427 5 391 5 324 4 126 4 189 3 189 3 378 3 639 3 945 2.5 1035 2.5 315 3.5 585 3 495 3 337 2 540 2 540 3 472 3 450 5 450
Initial and Final Rates Saponificeof Distn. tion No. Drops/min. 150-120 ... 160-120 ... 160-100 ... 120-100 ... 120-1 00 ... 120-100 452 130-100 371 160-120 316 200-120 278 210-120 273 200-120 280 160-120 280 200-120 271 160-120 261 140-120 252 180-130 243 160-120 234 160-120 236 190-120 205 180-140 198
Of residual gas, as measured by a Pirani gage attached to the still. The average distance between the distilling and condensing surface was 1 am.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 29, NO. 10
tion curves of dyes and vitamins from the oil are not appreciably sensitive to moderate divergence from uniformity so that this variation is not yet significant in practice. The low-boiling fractions of the constant-yield oil are pale yellow in color, odorless, but slightly bitter in taste. Those boiling above 180” C. are brownish yellow, odorless, and bland in taste. TABLE 1x1. DATAON CONSTANT-YIELD MIXTURET-175 -CompositionFraction of blend Weight T-170 used (Table 11) fra%on Crams
6 7 8
9 10 12 “ l3 16 l4
3.1 7.7 10.6 5.6 4.3 2.5 1.6 1.7 3.5 4.1
7 -
Fraotion
1
Residual gas Temp. Dressure
c:
Mm.
x
I10 190 210 T E M P E R A T U R E , OC
150
230
250
Weight
108 Cram*
7 8 9 10
1.4 1.3 1.2 1.2 1.2 1.3 1.5 1.7 1.8 2.0
2.2 1.9 2.5 2.9 3.3 3.8 4.0 3.5 3.0 2.9
16
250
1.2
7.3
6
130
FIGURB 2. YIELDCURVE
100 110 120 130 140 150 160 170 180 190
2 3 4 5
110
Distillation
Acknowledgment The authors wish to thank K. C. D. Hickman for suggestions and advice.
Literature Cited Burch, C. R., Proc. Roy. SOC.(London), A123, 271-84 (1929). Hickman, K. C. D., IND. ENG.CHEM.,29, 968 (1937). Hilditch, T. P., and Rigg, J. G . , S. Chem. SOC.,1935, 1774-8. Long, J. S., Kittelberger, W. W., Scott, L. K., and Egge, W. S., IND. ENG.CHEM.,21, 950-5 (1929). ( 6 ) Marcus, J. K., J. Biol. Chem., 80,9-14 (1928). (6) Washburn, E. W., IND.ENQ.CHEM.,25, 891-4 (1933); Washburn, E. W., Brunn, J. H., and Hicks, M. M., Bur. Standards J. Research, 2, 467-88 (1929). (7) Waterman, H. I., and Rijks, H. J., 2. deut. 01- u. Fett-lnd., 46, 177-8 (1926); Waterman, H. I., and Nijholt, J. A., Chem. Weekblad, 24, 268-9 (1927); Waterman, H. I., and Elabach, E. B., Ibid., 26, 469 (1929). (1) (2) (3) (4)
~
Constant-yield oil has been used extensively in this laboratory for the analytical distillation of vitamins A and D and for testing the purity of appropriate substances, such as dyes. It may be safely used in vitamin studies because its absorption in the ultraviolet is small and it contains no toxic substances to interfere with feeding experiments.
RECBWED June 1. 1937. Communication 632 from the Kodak Research Laboratories.
Soft Solder Fluxes Practice and Theory CLIFFORD L. BARBER Kester Solder Company, Chicago, Ill.
But first some of the practical phases of the flux problem should be discussed.
Types and Properties of Fluxes
T
H E literature on soft solder fluxes is sketchy, incomplete, generally unreliable, and seldom applicable to the real problems of soldering. For this reason the solder user is mired in that atmosphere of doubt, dogma, and confusion which has long enveloped the subject of solder fluxes. The purpose of this article is to relieve and clarify some of this existing confusion and at the same time to provide the user with information which is sound, practical, comprehensive, and directly applicable to his real needs.
Nature and Purpose of a Soldering Flux A soldering flux may be defined independently of theory as some agent which promotes or accelerates the wetting of a metal by molten solder. Soldering involves an alloy action between bare metals and it is the function of the flux to ensure a completely metallic contact; naturally, if metals cannot touch each other, they cannot alloy. To say that a soldering flux is a substance which “dissolves metallic oxides” is, after all, an assumption with respect to the theory of the fluxing mechanism rather than a statement of an observed fact. The exact mechanism of the flux reaction is not fully understood, and a satisfactory theory has yet to be advanced.
There is a general impression that soldering fluxes are active acids or that they owe their activity to an acid character; in fact, the terms “soldering flux” and “soldering acid” are used interchangeably by the trade. It is true that some fluxes are very mild acids; it is further true that certain others react acid by hydrolysis; however, some fluxes are not acid under any conditions. The general practice of attempting to activate a flux by the addition of mineral or other acids is of doubtful value. At most, the acidity of a soldering flux is very slight; the exact relation between the acidity of a flux and its fluxing effectiveness has never been definitely established. For practical purposes fluxes may be classified as follows: 1. The salt type, such as the chloride of zinc, ammonia, calcium, magnesium, aluminum, and certain other metals. Solutions of one or more of these salts are popularly known as acids. 2. The carboxylic acid type, such as stearic, oleic, palmitic, benzoic, tartaric, furoic, phthalic, and similar organic acids; these are often popularly classified as waxes. 3. The weak organic base type, such as aniline, urea, ethylene, diamine, acetamide, and certain other amines and amides. 4. Rosin.
