Microdetermination of the Formyl Group JOSEPH F. ALICINO, Squibb Institute for Medical Research, New Brunswick, N. J.
HIIX the microdetermination of the acetyl group is now widely used. !ittle attention has been paid to analysis of the formyl radical. Usually identification of the formyl derivative by means of carbon and hydrogen analysis is sufficient, but in certain critical cases an analysis of another constituent may be desirable. The acetyl determination should be valid for all volatile acyl groups, but since no reference to the application of this method to the formyl group was found in the literature, this determination was studied. Because it WMS felt that the reducing properties of formic acid might serve to distinguish it from the other volatile acids, the question of whether formic acid and bromine react quantitatively in 0.01 N solutions was investigated. It was found that the formyl group can be determined under the same conditiond as the acetyl group. The determination can be made specific by treating the distilled formic acid with an excess of bromine. Formic acid solution, 0.01 N , was pre ared and standardized by means of excess potassium iodate a n a potassium iodide, and 0.01 N bromine solution was prepared and standardized by titration of iodine from potassium iodide. This solution must be stored in a refrigerator and its factor checked frequently. An excesa of the bromine solution was added to a measured amount of formic acid in a stoppered flask and shaken thorou hly, and after 5 minutes the excess bromine was determined (Tabfe I).
TABLE I. DETERMINATION OF FORMIC ACID N
0.00882
N
Forrmc Acid
Bromine Solution
Calculated Excess
MI.
MI.
MI.
MI.
MI.
10.00 10.00 10.00 5.00 5.00 5.00
15.00 15.00 15.00 10.00 10.00 10.00
4.01 4.01 4.61 4.81 4.81 4.81
4.68 4.04 4.57 4.82 4.78 4.77
+0.03 -0.03 -0.04 +0.01 -0.03 -0.04
0.0102
*
Observed Excess
Difference
TABLE 11. DETERMINATION OB FORMYL Substance
Form I Fqund Formyl Found M Reducing M Jormic Acid Agent % %
Triformyl cholic acid Diformyl desoxycholic acid Cholesteryl formate &Beniyl-N-formyldl-cysteine 8-Bensyl-N-formyl-d-cysteine
S-Benryl-N-formyl-1-cysteine Methyl formmiline
17.18 17.30 12.56 12.66 7.01 0.88 12.38 12.20 12.05 12.15 12.20 21.a6 21.32
Formyl Calculated %
17.33
17.08
12.43
12.94
7.25
... ... ... ...
7.00 12.15 12.15 12.15 21.48
Determinatiom were run according to the Elek-Hart8 method for acetyl (8) on several formyl derivativaa whose purity wag checked by melting point and carbon and hydrogen analysis (Table 11). In a few instances where there waa available materid, the modified method wing the liberated formic acid as a reducing agent was followed. It WM obeerved and substantiated by the senior euthor (1) that cormtion for the amount of sulfur dioxide liberated from the saponifying agent is seldom necessary, if the procedure is carefully controlled. Therefore, freehly dietilled water can be used in the receiver where there is a question of the nature of the acid group. In this case, the dietillate is qusntitatively transferred to a stoppered h k , the properly prepared bromine solution is quickly added in e x m , and the exceBB is titrated as described. If both formyl and aoetyl may be pres-
ent, a total acid titration ahould first be performed, preferably on a separate sample or on an aliquot of the distillate.
Acknowledgments The author wishes to express his thanks to Oskar Wintersteiner for his advice and interest in this work. The cysteine derivatives were kindly furnished by J. A. Stekol.
Literature Cited (1) Elek, A., private communication. (2) Elek, A., and Hark, R. A,, IND.ENQ.CHEIY.,ANAL.ED.,8, 267
(1936).
Pipetting Apparatus W. G . SCHNEIDER, Mallinckrodt Chemistry Laboratory, Harvard University, Cambridge, Mass.
D
URING a recent research, it was necessary to withdraw
accurately aliquots of 2 and 3 cc., respectively, from a twophase liquid system containing 3 cc. of aqueous solution and 4 cc. of a chloroform solution. The solute, whose concentration in each of the two phases was to be determined, was highly toxic. In addition to the hazards involved in carrying out the operation by the usual pipetting technique, it waa difEcult to obtain a clean separation of the layers. The apparatus described below, while originally designed to 6ll these needs, has, because of its simplicity and eaae of operation, been found extremely useful for all pipetting operations, and particularly for pipetting strong acids and bases, toxic liquids, and volatile solvents. The apparatus provides smooth, accurate control, and the speed of pipetting is comparable to that by the usual technique. The brass cylinder, B (2.5 cm., 1 inch, in inside diameter), receives a threaded braas plug, A (threaded surface 2.5 cm., 1 inch, long)' 16 threads er inch have been found convenient. The c a r ' i t y of the cyyider assembly is 25 cc. Pyrex capillary tu ing (Zmm.), joined to the o posite end of the cylinder by means of a suitable cement ({hawinagan resin, Picein, or DeKhotinskycement), issealedtoaglass bulb, C, of 25-cc. capacity, and the latter joined to a further length of capillary tubing as shown in the diagram. D is a No. 1 one-holed stopper which receives the pipet. About 30 cc. of glycerol are introduced into the apparatus; air trapped in B can be removed by holding the apparatus on its right side and t w n g u plunger A . The glycerol besides Ebricating the threaded surface acts as a convenient air block, making the apparatus airtight. To o rate the apparatus, !he used is moistened and inpipet serted into sto per D. By turning A counterclocfhise, the liquid to be pipetted is lifted slight1 above the pipet mark, E. With t i e tip of the pipet resting against the side of the veasel containing the liquid, A A is turned slowly clockmse until the " liquid level reachea mark E. Delivery is then effected by clockwise rotation of A . Any volume of liquid from 25 cc. to less than 0.01 cc. can be accurately meaaured. A small-diameter, .knurled extension attached to dmk A may be found convenient for major adjustments, and will considerably re duce the time required for operation.
toE
