Kinetics of methanol-lactic acid reaction Reaction with 85% Acid RALPH A. TROUPE' AND KENNETH A. KOBE UNIVERSITY OF
.
TEXAS,
AUSTIN, TEX.
Kinetic data for the reaction of methanol and lactic acid were determined in a series of experiments using 85% reagen$ grade lactic acid and absolute methanol in sealed tubes. 'Variables studied were temperature, concentration of mineral acid catalyst, and mole ratio of reactants. It was found that the kinetic data for 85% lactic acid and methanol were represented by an equation of the form
Re
=
K
( A - &)(A- b
- Z)
where A - b is the original titratable acidity. The effect of the variables given above upon the rate constant, k, was studied and the results were correlated into a single empirical equation for the rate constant. Average percentage deviation of the values of k calculated by this equation from the actual values of k was about 8.7%. A flow reactor was constructed and operated to test the utility of the equation derived. Average percentage deviation of flow reactor results from those predicted from the equation was about 5%.
D
URING the past 15 years the United States has started
*
producing the purer grades of lactic acid, which were previously imported. This change was brought about not only because this country was cut off from its sources of supply by the war, but also because of the increased demand for these grades of the acid. This demand is principally due to the recognition of the usefulness of the two functional groups in one compound for the manufacture of plastics and synthetic resins and aa a valuable chemical intermediate (6). Several important methods of preparing the purer grades of the acid involve the formation of the methyl or ethyl ester from the crude acid or a crude salt of the acid and the corresponding alcohol ( I , b,4, IS,1 8 , I Q ) . This ester is then separated from the reaction mixture and hydrolyzed to the pure acid and the alcohol, which is recovered and re-used. The methyl lactate produced in this way has some demand itself both as a solvent and rn a chemical intermediate. In the design of equipment for carrying out these processes, fundamental data on the kinetics of the basic reactions involvedthat is, between lactic acid and methanol-are required. Despite the fact that both lactic acid and methyl lactate were first prepared in the nineteenth century and are being produced on a commercial scale today, no reference to the kinetic data exists in the literature. This is due in large measure t o the complexity of the reaction mixture and the difficulty of analyzing it. It is evident that the information needed includes a relationship expressing the effect of the process variables, temperature, catalyst concentration, and ratio of reactants on the specific reaction rate constant, variation of the density of the reaction mixture with temperature and composition, kinetic data on the reaction of methanol with the catalyst, and equilibrium constants for the esterification. In order to ensure the utility of the mathematical correlation, it should be tested in a flow-type continuous system patterned after one that might be operated on a commercial scale. 1
TEMPERATURE, OC.
Figure 1. Density of Reaction Mixtures
Studies on Rate of Reaction Materials Used. Reagent grade 85% lactic acid which assayed 72.55% titratable acidity and 85.67% total acidity (both reported as lactic acid) was used in the laboratory kinetic studies. This"materia1 was assayed by titration and saponification with standard sodium h droxide solution. Edible grade 80% lactic acid furnished by I. du Pont de Nemours & Company waa concentrated to 85.57% total acidity (as lactic acid) by evaporation under vacuum for use in the pilot plant investigation. Absolute methanol, also furnished by D u Pont and analyzing 100% by density and boiling point determinations, was employed in al1,these experiments. Analytical rea ent grade sulfuric acid analyzing 97.03% sulfuric acid was used as a catalyst in most of the tests.
6.
Determination of Densities of Reaction Mixtures. To determine the densities of the reaction mixtures at the temperatures of reaction, a modification of the method of Leyes and Othmer (IO) waa used. As in theprevious work, a thin-walled cassia flask of 100-ml. capacity, with a graduated neck of 10-ml. capacity, was employed and was first calibrated with water. An eguation based on t h k calibration was derived for the relationship between true and apparent densities:
-
d = (1.00395 0.0000493671)d' (1) where d is the true density, gram; per ml., d' is the apparent density, and tis the temperature in C.
Present address, University of Louisville, Louisville, Ky.
801
INDUSTRIAL AND ENGINEERING CHEMISTRY
802
Vol. 42, No. 5 ~~
Table I. Density of Reaction Mixtures at Various Temperatures Indicated Apparent True Temy., Volume, Densjty, Density, c. MI. d d, G,/Ml. -4. Calibration with r a t e r ; Weight of Water 99.5640 Grams 100.00 0,99564 20 0.99465 100.10 25 0.99345 100.22 30 0,99187 100.38 35 100.50 0.99069 40 0.98872 100.70 45 0.98676 100,90 5.0 0,98383 101.20 a0 0.98238 101.35 60 0.97948 101.65 65 0.97703 101.90 70 0.97136 102.50 80 0,96561 103.11 90 0,96290 103.40 95 0.9601% 103.70 99 Equation: d = (1.00395
B.
-
0.000049367t)d'
Reaction hlixtrire M/L = 4.0; Weight of Mixture 94.7205 Grains 20 100.00 0,94721 0.95002 25 100.40 0,94343 0.94899 40 101.80 0.93046 0,93230 GO 103 78 0,91271 0.91361 70 104.70 0.90469 0.90514 80 105.88 0,88460 0.89460 90 106,80 0.88690 0.88647 100 107.80 0.87867 0.87780
C. Reaction Mixture .M/L = 1.0; Keighr of Mixture 108.1730 Grams 20 40 60 80 100
100.00 101.73 103.30 105,zo 106,87
1.0817 1,0633 1.0472 1.0283 1,0122
1,0849 1.0654 1,0482 1,0283 1,0112
To determine the densities of the reaction mixtures, the flask was filled to the zero ?ark at 20" C. with a Tveighed amount r h e stopper was then sealed in the neck of the flask because some of the reaction temperatures were higher than the boiling point of the mixture. The flask was placed in a constant temperature bath until the volumetric reading on the flask remained a t a constant value for 5 minutes. From the apparent volume found in this manner and the equation given above, the true value of density was cald a t e d . In determining the densities in this manner it is assumed that the volume change during reaction is negligible. of the reaction mixture.
Temp.,
c.
D.
Indicated Volume,
Apparent Density,
True Density,
100.00 101.70 103.50 105.40 107.21
1.0172 1.0002 0.98282 0,96510 0,95884
1.02020 1.00218 0.98379 0.96510 0,94790
d, G . / M MI. d' Reaction Mixture M / L = 2.0; Weight of Mixture 101.7220 Grame 20 40 60 80 100
E.
Reaction Mixture M I L = 6.0; Weight of Mixture 91.0832 Grams 20 100.00 0.91083 0,91353 40 101.96 0.89341 0.80517 GO 103.95 0.87622 0.87709 80 105.98 0,85944 0.85944 100 108.26 0.84133 0.84050
F.
Reaction Nixture M / L = 8.0; Veight of Mixture 88.7963 Grams 20 100.00 0,88796 0.89059 40 102.02 0,87038 0.87210 GO 104.10 0.85299 0.88383 70 105.20 0.84407 0.84449 75 105.70 0.84008 0,84029 80 106.27 0.83557 0.83557 100 108.55 0.81801 0.81720
be calculated from the per cent sulfuric acid reacted and the original per cent of sulfuric acid: Equivalents/100 grams of solution = (200 - % reacted) (original %) (2) (100) (98) Equation 2 is related to the "apparent" equivalent weight as used by Leyes and Othmer ( I O ) in the following manner: Apparent equivalent weight = original % equivalents
(3)
A determination was also made for the reaction of hydrogen chloride with methanol at 100' C. The acid equivalent present a t time @lnaJ'be calcdated by: grams Of = (100 - % HCI reacted) (original %) (1001 (36.50)
(4)
Reaction of Methanol and Sulfuric Acid. Because a reaction between alcohol and sulfuric acid catalysts in esterification reactions has been reported (IO,I @ , a study was made of the rate of reaction of methanol with small amounts of sulfuric acid. These data were necessary in order that a correction for the amount of catalyst present in the reaction mixture at any time could be made for the equivalents of acid change as the sulfuric acid reacts to form methyl hydrogen sulfate
These determinations were made at each reaction temperature studied by adding approximately 0.5% of sulfuric acid to methanol, sealing the mixture in soft-glass ampoules, and placing the ampoules in a constant-temperature bath. At inteivals a tube was removed and chilled, and its contents were weighed and titratedwith0.1 N sodiumhydroxide solution using a microburet graduated in 0.01 ml. For the reaction between methanol and sulfuric acid the acid equivalents present a t time 8 can
TIME -HOURS
Figure 2. Rate of Reaction of Methanol and Sulfuric Acid at Various Temperatures and Hydrochloric Acid at 100' C.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
803
of 100O C. took approximately 1 minute, while to cool it from the bath temperature to 0' C. took approximately 4 minutes.
Effect of Variables on Rate The effect of temperature, catalyst concentration, and ratio of reactants on the reaction of 85% lactic acid with methanol is shown in Figures 3, 4, and 5. The run with 0,306%sulfuric acid catalyst breaks off sharply as the expected equilibrium value is approached and the data for longer periods of time show irregularities. This is undoubtedly due to side reactions, some of which have been reported by Rehberg (11).
Order of Esterification Reaction The data for the reaction of 85% lactic acid with methanol are given in Table 111. These data were tested in TIME-HOURS the established manner (6) to deterFigure 3. Effect of Temperature on Rate of Reaction of 85 % Lactic Acid with Methanol mine if they followed a first-, second-, Mole ratio approximately 4, catalyst concentration approximately 0.1% sulfuric acid or third-order reaction. The data di$ not resemble any of these processes, which is logical in view of the Reaction of Lactic Acid and Methanol. The lactic acid, complex nature of the reaction mixture. methanol, and sulfuric acid were weighed into separate flasks in Accordingly, an empirical equation which adequately the proper proportions. The contents of these flasks were then chilled in an ice bath, combined, and thoroughly mixed. - 4 ~ - represent the data was sought. This equation, obtained by following the usual mathematical standards (lb), took the proximately 8-ml. samples of the mixture were sealed in soft-glass ampoules and placed in a constant-temperature bath. form At intervals ampoules were removed from the bath, chilled in an ice bath, and broken open. Weighed aliquots were analyzed X for total lactic acid by a method previously reported (16). ke = (5) ( A - b) ( A - b - X ) In a separate experiment, in which thermocouples were sealed into tubes containing the reaction mixture, it was established that where A is the total lactic acid originally present, b is a constant no appreciable time lag occurred in heating or cooling the samples. which varies with the ratio of reactants, X i s the amount of lactic To raise the sample from room temperature to a bath temperature
Table 11. Reaction of Methanol with Mineral Acid Catalyst (Basis 1 gram of solution) MilliiMillimoles Time, equivalents HZs04 Hours of Acid Reacted Temperature 25' C., Catalyst 0.45% &SO4 0.0 4.0
7.0 16.0 19 0 24.0 40.0 66.0 135.0 256.0
0.00
99.1
Temperature 60' C., Catalyst 0.570% 0.0 0.25 0.50 0.75 1.00 2.00 4.00
27.00
Temperature looo C., Catalyst 0.548% HzSOa 0.1117 0.0 0.0561 0.05565 0.0560 0,05575 0.0563 0.05540
0.0 8.3 15.9 32.7 38.8 43.5 63.0 80.5 95.8 99.3 0.0 16.8 32.0 54.0 79.0 95.7 97.0 98.3
2.0 4.0 8.0 24.0 37.0 48.0 77.0
0.0 0.25 0.50 2.00
Time Hours'
Temperature 40' C., Catalyst 0.468% HzSO4 0.0 1.0
1.00 2.00 4.50
MilliMillimoles equivalents of Acid Reacted Temperature 80° C., Catalyst 0.541% HI SO^ 0.1104 0.0 0,0578 0.0526 0.0563 0,0541 0.0559 0.0545 0.0563 0.0541 0.0562 0,0542 0.0558 0 .:546
%
Reacted
0.0 48.5 74.5 85.5 92.1 97.5 97.5 98.6
0.25 0.50
0.75
%
Reacted 0.0 95.4 98.0 98.7 98.0 98.2 98.9 0.0 99.6 99.8 99.2
With Hydrogen Chloride. Temperature 100° C., Catalyst 0.450% HCI 0.0 0.0 0.167 22.9 0.333 41.7 0.500 54.5 1.0 75.5 2.0 88.2 14.0 9;7.0
INDUSTRIAL AND ENGINEERING CHEMISTRY
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acid converted in time e, B is the time of reaction, and k is the specific reartion rate constant.
Table 111. Xeaction Rate Data for 85570 Lactic Acid and Methanol Acidity, RI1. of 0.1 A' Base/Gram of Solution
In a differentiated form this equation i
Titratable Acid Lactic acid -t Lactic Concatalyst acid verted
I _
Tiliie. IIo11rs
In order to make the equation coni0.00 pletely applicable to the entire range of 0.23 0.50 variables it is necessary to repiesent b as 1.00 .. 2.00 .. a complex function of the mole ratio ,*.a0 of reactants. The equation thus de6.00 8.00 rived is so complex in nature as to limit 24,OO its usefulness. I t was found that if A -b is represented by the original titratable 37.44 0.0 36.07 acidity of the reaction mixture, a value 1.o 34.45 2.0 easily obtained, the resulting equation 3.0 32.24 33'42 4.0 represents the data well except for runs 30.40 6 .O 8 . 0 28.72 with mole ratios of 6 and 8. Un12.0 26.24 25.0 doubtedly, the mechanisni of reaction 20.75 48.0 15.93 changes with the ratio of reactants as, for the experiments with ratios of 6 and 0.000 36.80 8, the data are fitted better by an equa16.26 0.167 11.25 0.333 tionke = X/A(A - X ) than by Equa0,500 9.06 tion 5 . 7.58 1.000 2.000 7.05 Plots of X / ( A - b - X) against 4.000 7.61 time were made, with X data obtained from the smoothed curves of per cent 50.63 0.00 0.25 31.11 esterified, and using the values of origi0.50 23.88 nal titratable acidity for A - b (Fig18.58 1.00 16.24 2.00 ures 6, 7, and 8). Reasonably straight l5,81 3.00 4.00 15.40 lines were obtained in nearly every case 15.35 6.00 6.00 13.15 up to 90% or more of the equilibrium per cent reacted. The exceptions mere the run with 0.051% sulfuric acid cata24,7Y 0.000 11.83 0.167 lyst and the curves for the higher 7.49 0.333 6.07 0.500 ratios of methanol to lactic acid. 4.09 1.000 The run with 0.051% catalyst showed 3.30 2.000 2.97 4,000 a scattering of points. Inasmuch as in this run, takingthe average slope through 36.69 0.000 the points and the origin did not repre12.42 0.187 9.34 0.333 sent the trend of the data, the line was 8.13 0.500 drawn to represent the trend of the data 7.74 1.000 7.69 2.000 a8 aligned visually. In the case of the 7.98 4,000 higher ratios of methanol to lactic acid the curves exhibit a marked rise after the 0.00 63.37 43.65 first point or t-wo, rather than a fall. 0.25 36.55 0.50 This induction period has been observed 31.92 1.00 29.89 2.00 in other esterifications (2, I O ) . As 31.01 4.00 pointed out previously, the significance of this induction is probably that the mechanism of reaction is different foi the runs of higher ratio. Slopes of these curves were obtained, a8 in the previous work cited, by taking only the origin and the first point or two. Because the equation for an irreversible reaction is being applied to a reversible reaction, it is not surprising that the data deviate from straight lines above approximately 80% completion of the reaction. The deviation here is due to the increasing significance of the reverse reaction of hydrolysis. An examination of Equation 5 shows that the units in the ratio
X
A - b -
x)are immaterial as long as they are consistent but,
in order to obtain k in the units liters per (mole)(minute), the quantity A b should be expressed in moles per liter and 0 In minutes. The best straight line through the points (indhe
-
Vol. 42, No. 5
100' C., 0.0% 37.00 32.18 28.53 22.89 17.86 13.65 11.59 10.61 7.60
Polymer converted t o methyl lactate
3 Orig. total acid
Total Lactic Acid Converted, hIole/ 100 G. Soln.
I
Condr . ~ l
&Sod, J l / L = 3.88, L = 0.4366 4'.h 8.47 14.11 19.14 23.35 25.41 25.39 29.50
a,%
i:oo
0.653 0.525 0.410 0.313 0.265 0.243 0,172
1.40 3.50 4.90 5.35 5.83 6.02 6.10
o.Oit32 0.0987 0.1761 0,2404 0.2370 0.3124 0.3241 0.3560
1 3 R:I 2'2.60 40.40 53.00
65.70 71.;(l 74,1(J 81.50
25' C., 0.1058Yo I1$301, M I L = 3.82. I, = 0.44 37.22 35.85 i'.37 o.Sij o:tk 34.23 2.99 0,778 0.56 0.70 0,755 4.02 33420 32.02 5.20 0.728 0.78 1.25 0.685 30.18 7.04 1.30 0.648 28.52 8.70 26.05 11.17 L65 0.592 2.18 20.88 16.64 0.469 2.78 15.78 21.44 0.358
0,0355 0.0472 0.0398 0,0829 0.1003 0.1232 0.1882 0.2422
6.06 10.70 13.57 18.83 22.80 29.20 42.75 85.2(1
100' C., 0.198% HzSOa, .ll/L 3 3.97, L = 0.430 36.40 a:i1 16.06 26.34 0.373 0.257 3.40 11.05 23.35 3.65 8.86 27.54 0.206 4.26 29.02 7.38 0.172 5.04 29.55 6.85 0.159 5.46 7.41 0.172 28,99
O.ii65 0.2875 0.3119 0.3328 0.3459 0.3446
52 7ir 67.00 72.52 77.40 80 50 80 30
o.iisi
0.3064 0.3783 0.4149 0,4209 0.4268 0.4305 0.4357
3ti'.ko 51.90 63.65 69.80 70.90 71.70 72.50 73.40
1.33 2.21 2.46 3.00 3.50 3.67
0 , i419 0.1941 0.2108 0.2360 0,2489 0.2539
67.00 72 70 81.40 85.90 87 65
2:76 3.29 3.82 4.24 4.90 5.27
0.2671 0.3032 0.3196 0.3287 0.3358 0.3366
62'.b0 71.45 75.15 77.50 78.95 79.10
o.ii59 0,3129 0,3844 0,4219 0.4199
2i.00 42.05 51.60 56.60 56 50
100° C., 0,102% H&Oi, M / L = 1.97, L 60.42 31.01 ii.hi o.'s'az 0,400 23.78 26.64 0,310 18.48 31.94 34.28 0.271 16.14 0,264 15.71 34.71 0.237 35.12 15.3Cj 35.17 0.256 15.20 15.05 35.37 0,253 100' c., 0.097% &Sod, M I L = 7.5, 24.59 12.86 0.;05 11.73 0.255 7.39 17.20 0.206 5.97 18.62 0.138 3.99 20. GO 0,110 3.20 21.39 0,099 2.87 21.72 36.06 12.11 9.02 7.92 7.43 7.38 7.67
23.95 27.03 28.14 28.63 28.68 28.39
100' C., 0.1015% HzSOa, M / L = 0.902, L
63.19 43.55 36.43 31.82 29.79 30.91
19.64 26.74 31.37 33.40 32.28
0.585 0.400 0,427 0.400 0.415
4.6U
= 0.505
2:Ao 4.20 5.89 7.21 7.38 7.56 7.88 8.20
7, =
0.285 0.212 0.187 0.175 0.174 0,180
o.oioz
0.290 48.90
0.745 i'.& 4.55 7.07 8.79 9.71
region where the data approximated a straight line) arid the origin was calculated, from the average slope through the points and the origin with the exceptions noted above. Values of F: were then obtained by dividing the slopes of the lines by values of A - b, in moles per liter, which had been calculated from the original titratable acidity and the density values determined for the rea,ction mixtures.
Equation for Rate Constant I t was found that Iz varied with the catalyst concentration, the temperature, and the mole ratio of methanol to lactic acid. Previous work (6) has shown that the rate constant is proportional to the concentration of the mineral acid used as a catalyst
May 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
805
data. This method, which gives the equation for which the sum of the squares of the deviations is a minimum, Total Acidity, MI. of 0.1 N Base/Grams of Solution ti^ is used primarily because the square of Acid Titratable Acid Titratable Converted, an error is the measure of its improbLactic Acld verted to Mole/ ability. In the case of the variation of Time, acid + Lactio ConOrig. total methyl 100 G. % Hours catalyst acid verted acid lactate Soh. Conirerted specific reaction rate constants with the 100' C., 0.051% HtSOr. M/L = 3.88, L 0.436 different reaction variables, the differ0.00 37.08 36.98 ence in the value of the constant between 0.25 27.10 27.05 9.93 0.620 o:is o.iOe.9 24.9 0.50 21.26 21.21 15.77 0.486 3.06 0.1883 43.2 tjhe two ends of the scale may be as murh 0.366 3.93 0,2495 57.4 15.96 21.02 1.00 16.01 as twentyfold. Therefore, if the same nu0.24 0.3121 71.5 11.01 25.97 0.252 2.00 11.06 28.40 0,197 4.00 8.63 8.58 5.73 0.3413 78.2 merical deviation exists a t 0.0% catalyst 8.02 28.96 0,185 5.90 0,3486 80.0 6.00 8.07 6.03 0.3531 81.0 concentration as at 0.306% catalyst con0.176 8.00 7.75 7.70 29.28 centration the percentage deviation for 100' C., 0.0962% HzSO4, i M / L = 6.86, L 0.342 the 0.0% catalyst run is 20 times :is 0.000 29.16 28.96 0.167 15.57 15.47 i3'.49 0.453 o,iiie 44.30 great as that of the 0.306% catalyst run. 2.70 0.2144 62.80 18.74 0.299 10.32 10.22 0.333 For this reason Equation 7 and the others 3.22 ,0.2419 70.80 7.99 20.97 0.234 0.500 8.09 3.40 0.2656 0.169 77.75 5.80 23.16 5.90 1.000 which follow were derived so as to give 0.138 4.10 0.2836 83.10 4.80 4.70. 24.26 2.000 4.12 0.2904 85.00 4.04 24.92 0.118 4.000 4.14 nearly uniform percentage deviations from the curve (9). looo C., 0.1016% HCI, .M/L= 3.97, L = 0.430 In order to compare the catalytic a('3F.40 0.000 36.68 16.29 zo.ii 2:21 16.50 0.167 0,380 0.2232 52.00 tivity of hydrogen chloride with that of 10.93 0,254 25.47 3.25 11.09 0.333 0.2872 66.90 27.45 3.75 8.95 0.500 0.208 9.08 0.3120 72.50 sulfuric acid, a run was made with 28.71 4.25 7.69 0.179 0.3296 76.80 1.000 7.76 0.1015% by weight of hydrogen chloride 29.32 5.02 . 7.08 7.11 2,000 0.165 0.3434 79.80 29.58 6.82 5.44 6.84 4.000 0.159 0.3502 81.50 as catalyst, a mole ratio of reactants of 29.51 6.89 6.90 5.73 0.3524 82.00 0.160 6.000 29.43 6.97 6.98 5.85 0.162 8.000 0.3528 82.05 approximately 4, and a temperature of 100" C. Because the acid catalysts are 0,000 36.88 36.66 present in such small amounts, the hy0.167 22.34 22.24 14.42 0.513 I:& o.iio5 37,'l drogen ion concentration will be approxi16.12 0.333 16.23 20.54 0.374 2.36 0.2290 53.0 0.500 12.47 12.36 24.30 0.286 3.88 0.2818 65.2 mately equal to the normality. Refer1.000 9.14 9.03 27.63 0.210 4.32 0.3195 73.9 2.000 7.90 7.79 28.87 0.181 5.23 0.3410 78.8 ence to Table I1 shows that in the case of 4.000 7.34 7.23 29.43 0.168 5 0.3500 81.0 a run with 0.198% sulfuric acid catalyst 8.000 7 .45 7 .35 29.31 0.171 6 .. 5 07 9 0.3540 81.8 at 100" C. the acid equivalent per 100 80' C., 0.1012% HzSOa, M/L 3.92, L = 0.4325' grams o f , solution is approximately 0.0 36.84 36.63 0.5 19.76 19.66 1G.97 0.255 1:68 0.1855 42.9 0.00203 throughout the run. With 1.o 14.21 14.11 22.52 0.327 3.06 0.25j.8 59.0 0.1015% hydrogen chloride as catalyfit 11.70 24.93 1.5 11.80 0.271 3.58 0.2801 66.0 2.0 10.30 10.20 26.43 0.236 3.70 0,3013 69.5 at 100" C. the acid equivalent decreases 3.0 9.33 9.23 27.40 0.213 4.00 0.3140 72.5 4.34 0.3308 76.5 as the run progresses (refer to Table 11). 4.0 7.99 7.89 28.74 0.182 6.0 7.46 77..3263 29.27 0.170 4 . 7 6 . 0.3403 7 8.6 Because values up to 1 hour were taken 8 .0 7.33 29.40 0.167 4.77 0.3417 79.0 to find k, a weighted value of the acid 12.0 6.92 6.82 29.81 0.158 5.44 0.3626 81.5 equivalent over the first hour of reaction 40' C.. 0.1011% HzSO4, IM/L = 3.87, L - 0.436 was calculated. The value of 0.00209 0.0 36.95 32.10 1 .o 4.85 0.737 0:io 0.6525 12.00 was used to calculate the normality. 29.15 2.0 7.80 0.669 1.65 0.0945 21.60 26.74 3.0 10.21 1.80 0.614 0.1201 27.60 An examination of Table I11 shows that 24.53 4.0 12.42 0.562 1.88 0.1430 32.80 21.71 the kinetic data for the hydrogen chlo15.24 6.0 0.498 2.01 0.1725 39.50 20.11 8.0 16.84 0.461 2.25 0,1909 43.80 ride-catalyzed run are almost identical 12.0 18.09 18.86 0.415 2.36 0.2122 48.65 13.94 24.0 23.00 0.320 2.94 0.2594 59.50 with those of the 0.198% sulfuric acidcatalyzed run. The ratio of the normali60' c., 0.1012% HzS04. iM/L = 3.92, L = 0.4325 0.0 36.89 36.68 ties of these catalysts indicates that the 29.20 29.07 0.5 7.bl 0.'6j3 i:i7 20.3 hydrogen chloride should have a catalytic 1 .0 24.74 24.63 12.05 0.570 1.48 31.3 19.93 19.82 2.0 16.86 0.459 1.92 activity equal to 103% of the 0.198% 3 .O 17.36 17.26 19.42 0,399 2.56 15.76 4.0 15.86 20.92 sulfuric acid catalyst. This result seems 0.365 2.76 14.40 5.0 14.50 22.28 0.333 2.80 to be within the limits of experimental 13.42 13.31 6.0 23.37 0,308 2.90 11.56 11.46 8.0 25.22 0.265 3.26 accuracy. 12.0 9.72 9.62 27.06 0,222 4.42 24.0 7.57 7.47 29.21 0.173 In the case of the effect of ratio of re4.96 actants on the values of k, it has been reported (IO,17) that IC is proportional to the concentration of the organic acid. or to the hydrogen ion concentration in the solution. A plot of Because proportionality between IC and the catalyst concentrathe values of k against the concentration of the sulfuric acid tion has already been established, the effect of the ratio of recatalyst, C, in weight per cent of the total mixture, as shown in actants on a basis free of the effect of the catalyst is desired. Figure 9, reveals a linear relationship for values of C between This may be achieved by plotting (k a ) / C against the mole 0.0 and 0.306% sulfuric acid. This relationship for a mole ratio ratio of methanol to lactic acid, ( M I L ) ,where a is the value of IC of methanol to lactic acid of approximately 4 and a temperature corresponding to 0% catalyst concentration. Here again a subof 100' C. is represented by the equation: stantially linear relationship exists (Figure 10) for values of M /L from 0.9 to 7.5. For a temperature of 100' C. this line may be k = 0.2593C 0.00435 (7) expressed by the equation: In scientific work the method of least squares is extensively k - --a 0.08750(M/L) - 0.08955 used to calculate the constants in an equation to represent the (8) Table 111. Reaction Rate Data for 85% Lactic Acid and Methanol (Contiwed)
pzp -
.
I "
-
+
-
9
INDUSTRIAL AND ENGINEERING CHEMISTRY
806
Vol. 42, No. 5
k As a ratio this becomes 2-= kiw
10(1081369 - 3139 3 , T ) ___ 314 3 Combining this ratio with the catalyst-mole ratio expression for k gives the equation k
=
[O.O8750(13f/L)C 0.004351
[
- 0.08955C +
~O(lO.Sl369
-
]
3139 3 /T)
314.3
(11)
where k is the reaction rate constant, liters per (mole)(minute), M I L is the ratio of moles of methanol to moles of lactic acid, C is the weight per cent sulfuric acid catalyst, and T is the temperature in degrees Kelvin. The effectiveness of Equation 11 in representing the experimental data is shown in Table V, 11hich gives a comparison of the Of Obtafned from the data and Equation 5 with the values of k obtained from Equation 11. The average percentage deviation, including all runs, is 867%.
- HGURS
TIME
Figure 4. Effect of Catalyst Concentration on Rate of Reaction of 85% Lactic Acid with Methanol Mole ratio approximately 4 at looo C.
With temperature, it is well k n o m ( 6 ) that log k plotted against the reciprocal of the absolute temperature should yield a straight line. Such was found to be the case (Figure 11) over the range of temperature from 25 ' to 100 ' C. with a mole ~ a t i o of reactants of approximately 4 and a catalyst concentration of approximately 0.1% sulfuric acid. These data may be expressed by the equation: log 104k = 10.91369 - 3139.3/T
I'(
Mechanism of the Reaction Mechanisms for mineral acid-catalyzed esterifications ai e often derived in terms of complexes between alcohol and catalyst This mechanism was &t reported in the work of Goldschmidt ( 7 ) and later established more completely by the work of Smith (24). Unfortunately, in this current work no basis for comparison with the principles established by Goldschmidt exists. The work of Goldschmidt and of Smith was performed in a narrow
where 2' is the temperature in degrees Kelvin. From these data the energy of activation was calculated as 14,350 calories per mole. After evaluation of the role played by the different variables in the reaction on the valut. of the rate constant, all these variables \$ere assembled in one empirical equation. This was done by taking the expression involving the catalyst concentration and the moleratio of reactants at 100"C. (Equation 8) and applying the temperature relationship to this as a proportionality factor. The temperature relationship (Equation 9) may also be expressed in the form: fC
X 104 = 10(i0.91369-3139
3 /TI
(10)
Because one run, that at 100" C., is common to both equations, this may be used as a basis for the proportion. At 100" C. Equation 10 beconies kloo x 104 =
t
3139 3
io(lo.giae9-
313)
10(10.91369
- 3138 3 / T ) .
3
4
TIME
Figure 5 .
while a t temperature 1' it is kT X lo4
I 2
=
5
6
7
I
J
- HOURS
Effect of Mole Ratio of Reactants on Rate of Reaction of 85q0 Lactic Acid with Methanol Catalyst concentration approximately 0.1 Z sulfuric acid at 100" C.
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
May 1950
h
TIME -HOURS
Figure 6. Relation between X / ( A - b - X ) and Time at Different Temperatures Catalyst concentration approximately 0.1% and mole ratio approximately 4
,
I
/I d
M/L 1.97
21jv
M/L w o k
-~
I'
00
I
2
3
4 5 TIME -HOURS
5
I
7
Figure 8. Relation between X / ( A - b - X ) and Time for Various Mole Ratios of Reactants Temperature 100° C. and approximately 0.1% catllyrt
1
I
I
0.3
I
QI C, WEIGHT PER CENT0.2 %SO,+
Figure 9.
Variation of Specific Reaction Rate Constant, k, with Catalyst Concentration, C
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
$08
Table IV. Temperature Series Time, X hours ( A b X) 1000 C.
- -
1.025 2.31 3.51 4.63 6.90 9.32 13.10 13.85
40' C.
25' 1.000
2.000
3.000 4.000 6.000 8.000 12.000 24.000
Time X houri ( A b X ) 0.306% HsSO4 0.167 2.85 0.333 5.30 0.500 7.80 1,000 10.30 2.000 13.50 4.000 14.05
- -
1.80 3.75 5.55 7.45 9.10 10.65 19.10 17.70
0.105% His01
60' C.
1.000 2.000 3.000 4.000 6.000 8.000 12,000 24.000
Catalyst Series
0.167 0.333 0.500 0.667 0.833 1,000 2.000 4.000
80' C.
0.500 1,000 1.500 2.000 3.000 4.000 6.000 8.000
Data for Derivation of
0.1655 0.343 0.481 0.632 0.875 1.07 1.35 2.35
C. 0.0575 0.105 0,145 0,191 0.286 0,367 0.525 1.02
0.167 0.333 0.500 0.667 0.833 1,000 1.500 2.000 4.0:)O 8.000
0.895 2.04 3.05 4.11 5.25 6.47 9.60 13.30 21.10 28.10
0.250 0.500 1.000 2.000 4.000 6.000 8.000
0.485 1.04 2.15 5.41 12.00 16.40 21.20
0.1015% HC1 0.167 0.333 0.500 1.000 2,000 4.000
c, wt. %
x- -
M / L 1.97 0.250 0.500 1.000 2.000 3.000 4.000
Comparison of Actual and Calculated Values of k
Table V.
k
Ratio of Reactants Series Time hours' ( A b S) M / L 0.902 0.250 0..5!8 0.500 0.982 1.000 1.66 2.000 2.01 4.000 1.98
0.77 1.57 3.00 4.63 5.06 5.75
Vol. 42, No. 5
Temp., Cataa C. lyst M/L 0.0000 100 3.88 0.0510 3.88 100 3.95 100 0.1050 3.97 100 0.1980 4.05 100 0.3060 0.0970 7.50 100 0.0962 5.85 100 0.1020 1.97 100 0,1015 0.902 100 0.1012 3.92 80 0.1012 60 3.92 0.1011 40 3.87 0.1058 25 3.82 a From Equation 11. b From Equation 5.
k, Liters/(Mole)(Min.) __ CalcdSa 0,004350 0.017100 0.031238 0.055399 0 .OS6360 0.058320 0,044977 0.012798 0.010089 0,003272 0.002925 0.0007 193 0.0002303
Actualb 0,0138400 0,0043456 0.0317300 0,0559000 0.0853080 0.0672440 0,0449400 0.0107155 0.0041 116 0.0114330 0.0025150 0.0007514 0.0002279
Difference $0.0000044 $0,0032600 -0.0004920 -0.000~010 $0.0000520 -0.0089240 $0.0000320 +0.0020825 -0,0008396 -0.0013440 +0.0004100 -0.0000320 f0.0000024
Yi
D ~ ~ , ~ ~ . tion 0.1u 23,60 1.55 0.90 0.06 13.28 0.07 19.42 20.40 11.65 16.30 4.25 1 05
X / L 3.95 0,167 0.333 0.500 0.667 0.833 1.000 1.500 2.000 4.000 8.000
0.896 2.04 3.05 4.11 5.25 6.47 9.60 13.30 21.10 28.10
M I L 5.85 0.167 0.333 0.500 1.000 2.000
1.10 2.85 5.07 11.05 47.0
M / L 7.50 0.167 0.333 0,500
1.000
1.36 3.74 6.00 23.80
1.72 3.74 6.00 9.58 16.68 25.40
I t can be seen that these two reactions are interdependent and that the mechanism of the reaction is probably a complex function of the lactic acid concentration. It has been previously noted that the mechanism of the reaction changes with the higheT ratios of reactants. It is recognized that more complex mechanisms may be entrring into the formation of the methyl lactate, but consideration of these has been eliminated on the basis of previous work--for example, methyl esters of the polylactylic acids may be forming, but according to Jungfleisch ( 8 ) it is impossible to produce these in the presence of excess alcohol and, if they happen to be present, the alcohol will cause them to revert to methyl lactate. This rules out not only the possibility of esterification of the polylactylic acids but also the possibility of alcoholysis of the polylactylic acids. Another reason for minimizing the possibility of the more complex esters is that at equilibrium so little polv-
0%
0.6-
/
range of temperature, with anhydrous reagents, and with low concentrations of acid. In working with lactic acid there is approximately 0.85 mole of water per mole of lactic acid at the start; the temperature range investigated was from 25" to 100 ' C., and the acid concentrations were higher. In addition, i t is apparent that several reactions must be taking place simultaneously because of the complex nature of the lactic acid. Because of the complexity of the problem no mechani*m has been proved for the reaction between lactic acid and mcthanol. It is believed that two reactions predominate: 1. The esterification of the monomeric lactic acid with metha1101. Because of the large amount of water originally present, &he reverse reaction of hydrolysis probably competes with this fcirward reaction
CHsCHOHCOOH
+ CH2OI-I +
CHaCHOHCOOCH3
+ HzO
(12)
The hydrolysis of iactic acid condensation polymers to n!onomeric lactic acid. This probably takes place in several stages, but may be summed up as: 3.
HO
[lH3 ] H-coo
n
H
+ (n - l)HzOn-+ CH&HOHCOOH
(13)
M/L
Figure 10. Relation between Ratio of Reaction Rate Constant to Catalyst Concentration, (k u ) / C and Mole Ratio of Reactants, M I L , at 100' C.
-
May 1950
INDUSTRIAL A N D ENGINEERING CHEMISTRY
809
Table VI. Equilibrium Constants for Reaction of 85% Lactic Acid with Methanol Temperature Series, M / L Approximately 4, Catalyst Approximately 0.1 % H&Oi Equilibrium Tem erature, Constant,
c.
K
2.69 3.04 2.85 2.95 2.85 Av. 2.88
100 80 60 40 25
Catalyst Series, M / L Approximately 4, Temperature 100' C Weight
%
Catalyst
2.52" 2.75 2.69 2.96 2.75 2.79 Av. 2.79 Proportion Series, Temperature 100' C., Catalyst Appmimately 0.1% HnSOi
$0~24'
oho26'
oAoa8'
do030
'
&32'
a0034'
'
M/L 7.50 5.85 3.96 1 97 0 902 0
2.39 2.62 2.69 3.64 4.96
Omitted from average of this group
l/T
Figure 11. Relation between Reaction Rate Constant, k, and Reciprocal of Absolute Temperature, 1/T
lactylic acid exists that it would be virtually impossible to have any measurable amount of polylactylic esters.
A 20-am ere voltage regulator controlled the output of the heater on t i e first section, which was designed to bring the reactants to reaction temperature and maintain this temperature. A 5-ampere voltage regulator was used to control the output of the heater on the second and third sections, whose function was to maintain the reaction temperature. The end of each section was equipped with a thermometer well in which was inserted a calibrated centigrade thermometer reading to 110" in 1 O increments. 4
Equilibrium Constants
l
The equilibrium constants for the 85% acid were obtained by keeping samples of the reaction mixture in the bath until the composition became constant.
CONDENSERL
(methyl lactate)(water) K= (lactic acid)(methanol)
.
Table VI shows that temperature and catalyst concentration have no appreciable effect on the equilibrium constant in the ranges studied. However, a definite trend can be seen when the ratio of reactants is varied. The average value of the equilibrium constants for all runs with the 85% acid is 2.98. A considerable variation of the equilibrium constant with changing proportions of reactants was noted in the esterification of butanol with acetic acid (IO) and in later work in which 44% commercial lactic acid was used. Hence the variation is not due to the presence of polylactylic acids.
Pilot Plant Investigation In order to test the applicability of the specific reaction rate equation in designing flow reactors for carrying out the esterification on a commercial scale, a small pilot plant was designed and erected. Construction. The reaction mixture was fed to the reactor from 4-liter aspirator bottles by means of a duplex reciprocating The reactor was constructed of approx/mate!y 21 feet :?%inch stainless steel pipe divided for convenlence into three sections. These sections were wrapped with '/pinch asbestos paper, wound with Nichrome resistance wire, over which another ayer of '/*-inch asbestos paper was placed, and the whole was finally covered with 1.25-inch standard 8.5% magnesia pipe lagging. For the first section 25 feet of No. !8 gage Niohrome wire was used; for the second and third sections a total of 20 feet of No. 26 gage Nichrome wire w m used.
L!n
&---I-
FLASH TANK
Figure 12. Line Diagram of Pilot Plant
Discharge from the reactor was through a 0.5-inch needle valve into a copper flash tank. This tank, which was 6 inches in diameter and 10 inches high, was equipped with a reflux condenser to condense any flashing vapors. The lower 3 inches of the tank were jacketed with an ice bath to cool the products which were withdrawn from the bottom of the tank. The effective reactor volume was calculated from the dimensions to be 2400 ml. Operation. The reactants were measured out and stored in separate bottles which were chilled in ice. Water, mixtures 0% water and methanol, and finally some of the reaction mixture itself were pumped through the system while temperature, operating pressure, and rate were being adjusted. The pressure, maintained on the system to keep it entirely in the liquid phase, was approximately 40 to 50 pounds per square inch gage. Because of lack of automatic control it was not always possible to achieve exactly the temperature desired, even though it was possible to maintain the temperature of the system at a constant value during the run. When the system was operatin satisfactorily, the chilled reactants were combined, samplef for analysis, and passed through the system.
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
810
Table VII. Analytical Data from Reactor Runs pOIY-
Acidity, M1. of 0.1 N Base per Gram of Solution Titratable Acid TitCataJle Total Lactic ,ACldverted to lactic acid+ Lactic Con- Orig. total Methyl acid catalyst acid verted acid Lactate 37.70 37.50 44,25 19.73 19.83 17.77 0.446 2.09 37.70 37.50 44,25 19.10 19.00 18.50 0.435 2.23 37.88 37.60 44.37 11.51 11.35 26.25 0.256 3.42 30.20 30.00 35.41 15.20 15.10 14.90 0.425 1.88 30.20 30.00 35.41 16.65 16.75 13.35 1.84 0.470 37.59 37.99 44.35 9.14 8.94 28.65 0,202 3.10 37.99 37.59 44.35 8.97 8.77 28.82 0,198 3.32 37.69 37.59 44.35 27.29 27.34 10.30 1.11 0.615 24.85 24.65 29.14 14.70 9.95 14.80 1.03 0,505 37.15 37.35 43.90 14.25 23.00 22.90 1.48 0,523 37.72 37.52 44.26 20.82 16.70 20.92 2.48 0.471 37.52 37.72 44.26 15.71 15.61 21.91 3.58 0.353 37.62 37.82 44.46 15.96 21.76 21.66 1.73 0.488 37.90 37.60 44.37 15.90 21.85 15.75 2.94 0.355 38.20 38.10 4 5 , 05 25.52 12.58 I .41 25.57 0.567
c",",'.
Run NO. 1
2
3 4 5 6
7 8
9 10 11
12 13 14 15
Feed Product Feed Product Feed Product Feed Product Feed Product Feed Product Feed Product Feed Produot Feed Product Feed Product Feed Product Feed Product Feed Product Feed Product Feed Product
Total Lactic Acid Converted Mole/ 100 G. Soh.
Converted
0,1986
44.9
%
0.2073
46.8
0.2967
67.0
0,1678
47.3
0.1519
42.8
0.3175
71.6
0.3214
72.5
0,1141
25.8
0.1098
37.7
0.1573
35.9
0.1918
43.3
0,254R
57.5 39.8
0.1769 0.2479
5F.0
0,1399
31.0
Catalvat. concentrations were varied from 0.05 to 0.205% by weight of sulfuric acid based on the weight of thr mixture, and one run was made with 0.1% by weight of hydrogen chloride. The specific reaction rate constants were calculated for each set of conditions using Equation 11. The constants thus calculated were substitutedin Equation 5 and the equation was solved for X (the amount of acid reacted). The value of time, e, was obtained by dividing the flow rate in milliliters per minute a t the operating temperature into 2400 ml., the reactor volume. The calculated values of X and those obtained from the analysis of the pilot plant product are presented in Table VIII. Arerage percentage deviation 13 4 91%.
Nomenclature A -b
original titratable acidity, moleq per liter a = constant, corresponds to value of k for 0% catalyst C = weight per cent catalyst based on total of mixture ...... weieht . . ~ .~ ~ ~ .. .. K = equilibrium constant k = specific reaction rate constant, liters per mole-minute L = moles of lactic acid per 100 grams of solution Jf = moles of methanol per 100 grams of solution T = temperature, degrees Kelvin t = temperature, degrees Centigrade X = moles of lactic acid converted at time e, per 100 grams of solution 6 = time, minutes or hours, as specified
Table V I E Comparison of Actual Yields of Methyl Lactate with Those Calculated Using Equations 11 and 5 L.
Vol. 42, No. 5
-
A b, Residence C, Mole/100 Grams wt. % Moles/ 70 Run Temp., Time, X , calcd. X , exptl. Diff. Liter Catalyst Min. No. 0.032412 3.304 0.1975 0.1986 0 .56 3.78 0.103 102 10.40 1 0,032412 3.304 -0.63 0.2060 0.2073 3.78 0.103 11.45 102 2 0.052479 3 . 3 3 1 .92 0,2910 0.2967 3.76 0.1OOQ 19.60 3a 100 0.1632 0.1673 0.034065 2.54 -2.82 5 . 5 5 , 0.100 16.32 100 4 0 , 1 5 4 0 0,1519 0,034065 2 . 5 4 + 1 .38 5 . 5 5 0,100 15.40 5 100 0.2875 0,3175 0.059293 3.33 -9.45 3.76 0.205 16.38 102 6 8 . 52 0 , 2 9 4 0 0,3214 0.053417 3 . 3 3 0 , 2 0 5 3.76 7 20.20 100 0.1225 0.1141 0.016320 3.33 $7.35 3.76 0.050 8.90 100 8 0,1130 0.1098 0.054525 2 . 0 3 + 2 . 99 7.45 0 . 1 0 0 7.72 9 98 3.28 +7.10 0.1685 0.1573 0.026258 3.83 0.095 9.66 99 10 + 3 . 75 0 . 1 9 9 0 0.1918 0.024342 3.34 3 . 7 8 0.100 13.95 97 11 0,2700 0.2549 0.028470 3.32 3.78 +5.92 0.100 27.30 12 100 0 , 1 8 2 2 0.1769 0.016450 3 . 3 7 3.74 + 2 . 99 0.100 18.22 13 90 -1.57 0,2440 0.2479 0.040270 3.33 3.76 0.150 13.88 14 100 0,014970 0.1632 0.1399 f l 6 . 7 0 3 . 3 8 5 3 . 6 6 0 . 0 5 0 15.50 15 98 a Catalyst HC1. k calculated for this run by substituting for C weight per cent of sulfuric acid equivalent to normality of hydrogen rhloride present.
c.
=
Literature Cited (1) Bannister, W., U. S. Patents 1,695,449 (Dec. 18, 1928), 2,029,694 (Feb. 4, 1am) &""",.
( 2 ) Berman, S., hlelynchuk, A. 8.,and
Othmer. D. F.. ISD. EXG.CHEM.. 40, 1312'(1948).' (3) Filachione, E. M., and Fisher, C . H., Ibid., 38, 228 (1946).
When the pumping of the reaction mixture into the system was started, temperatures were recorded periodically until the run was finished. After approximately 2400 ml. of this batch had passed into the reactor, and at intervals of from 5 to 10 .minut,es thereafter, a sample of the product was taken and stored in a numbered bottle, submerged in an ice bath, until analyzed. Rates of flow were taken to correspond to these samples by measuring the amount and temperature of the product collected over definite intervals of time. These rates were converted to rates at the reaction temperature by use of the density values found previously. Analytical procedure was identical with that used in t'he kinetic studies.
(4) Filachione, E. M,, et al., Ibid., 37, 388 (1945). ( 5 ) Fisher, C. H., and Filachione, E. M., Bur. Agr. Ind. Chem., Bull. AIC-178 (May 1948). (6) Glasstone S.,"Textbook of Physical Chemistry," Sew York, D. Van Nostrand Co., 1946. (7) Goldschmidt, H., et ul., 2. physik. Chem., 60, 728 (1907); 81,
Pilot Plant Results
30 (1912); 143, 134, 143, 278 (1929). (8) Jungfleisch, E., and Godchat, M., Compt. rend., 144, 425 (1907). (9) Kobe, K. A., Petroleum Refiner, 28, No. 1 , 8 3 (1949). (10) Leyes, C. E., and Othmer, D. F., IXD.EKG.CHEM.,37, 968 (1945). (11) Rehberg, C. E., Faucette, IT. A , and Fisher, C. H., Ibid., 36, 469 (1944). (12) Running, T., "Empirical Formulas," New York, John Wiley & Sons. 1917. (13) Schopmeyer, H. H., and rlrnold, C. R., U. 8. Patent 2,350,370
A series of 15 runs was made in which mole ratio ( M I L ) of reactants, the catalyst concentration, and temperature were . . varied. Because 100" C. was the highest temperature investigated in the laboratory, most of the pilot plant rim were made a t o r near this value. The one exception was the run at 900 C . which wa8 made to test the temperature factor in the equation for k. Mole ratios from approximately 4 to approximately 8 were used, as this was judged to be the most feasible range for commercial practice.
(14) Smith, H. A., J . Am. Chem. Soc., 61, 264 (1939). (15) Suter* c. M., and Obertp E*,Ibid., 677 (1934). (16) Troupe, R. A., and Kobe, K. A., Anal. Chem., 22, 645 (1950). (17) Watson, H. B., "Modern Theories of Organic Chemistry," London, Oxford Press, 1937. (18) Mreisberg, 6. M., et al., U. 8. Patents 2,290,926 (July 28, 19421, 2,406,648(Aug. 27, 1946), 2,390,140 (Dec. 4 , 1945),2,434,300 (Jan. 13. 1948). (19) Wenker, H.', Ibid., 2,334,524 (NOT-.16, 1943). RECEIVED M~~ 21, 1940.
(June 6. - , 1R441. ~ ~~
~~~~
-
~
563
