THE USE OF METALLIC POTASSIUM IN DETERMINING HALOGENS IN BENZOYL DERIVATIVES.

By C. H. MARYOTT.

A METHOD for the estimation of halogens in organic compounds by reduction with sodium and alcohol was described a few years ago by Stephanoff (Ber., 1906, xxxix., 4056). The writer recently attempted to use this method in determining chlorbenzol, but the results obtained were very irregular and unsatisfactory. Before enough sodium had been added to effect complete reduction, the liquid became pasty owing to the separation of sodium ethylate, and this localised and greatly hindered the action of the sodium. By increasing the amount of alcohol above that recommended by Stephanoff, the sodium ethylate could be kept in solution, but the large volume of liquid retarded the reduction, and thus increased both the time and the amount of sodium required. In all cases the results of the analyses were low.

A failure to obtain satisfactory results with Stephanoff's method has likewise been reported by Bacon (Journ. Am. Chem. Soc., 1909, xxxi., 49), who, however, devised a modification of the method, in which accurate results were obtained by heating the mixture for an hour after the solution of the sodium, thus utilising the action of the sodium ethylate upon the halogens. Bacon's method was not tried by the writer, as the article cited came to his attention after the completion of the experiments described below. The long time required, about two hours, would seem to be a disadvantage, and the fact that certain of the benzoyl halogen derivatives, such as monochlor- and monobrombenzol, are attacked, but little, if at all, by boiling with sodium ethylate, a possible source of error in

the method.

(NOTE.-The writer boiled monochlor- and monobrombenzol in a concentrated solution of sodium ethylate for three hours, but failed to get any test for halogens upon acidifying and adding silver nitrate. Bacon states in his article that he was unable to convert monobrombenzol into phenetol by heating with sodium ethylate, although 25 per cent of the chlorine was removed from hexachlorbenzol by the same treatment).

The use of potassium instead of sodium as a means of obtaining a more rapid reduction was suggested to the writer by Prof. R. G. Van Name, and upon trial proved to be a great improvement. As the action of potassium upon alcohol is very energetic, a mixture of one volume of 98 per cent alcohol with two of thiophene-free benzol was employed. The presence of thiophene had to be avoided to

prevent the formation of potassium sulphide, which would interfere in the subsequent estimation of the halogen. The reduction was carried out in an Erlenmeyer flask, and very little heating was required, so that a plain glass tube about 50 cc. in length, without water cooling, served as a condenser.

The test analyses given below were carried out as follows:-The substance was weighed out in the Erlenmeyer flask, 10 to 15 cc. of the alcohol-benzol mixture added, and the potassium, in small pieces, gradually dropped in through the tube. The weight of potassium required was about ten times that called for by the equation C6H5Cl + 2K+C2H5OH - C6H6 KCI C2H5ÖK. (Stephanoff's method calls for twenty-five times the theoretical amount of sodium).

A small amount of potassium ethylate usually separated out during the action of the metal, but seemed to have no bad effect upon the reduction. After the action had become less vigorous, about 2 cc. of alcohol were added, the flask carefully heated, and gently shaken from time to time until the potassium was all dissolved. The contents were then shaken with water, the water layer acidified with nitric acid, and the halogen precipitated and weighed as the silver salt. The use of Volhard's volumetric method in estimating the halogens, as done by Stephanoff and Bacon, would, of course, have been feasible, though somewhat less accurate. The time required for an analysis, exclusive of weighings, was about twenty-five minutes. analyses gave the accompanying results. With the exception of No. 8 the agreement is satisThe low result here is doubtless due to the factory. use of an insufficient amount of potassium, as only six The chlorbenzul times that required by theory was added. was twice re-distilled and that portion distilling between 1315° and 1317° used in the analyses.

A series of

The results are very concordant but slightly high, probably due to impurity in the brombenzol, as the sample used was a commercial product once re-distilled. The material used was Kahlbaum's product once recrystallised from hot benzol.

To test the relative efficiency of sodium and potassium in their capacity as reducing agents, an analysis of chlorbenzol was carried out exactly as above described except that sodium (ten times the theoretical amount) was used in place of potassium. Only 84 per cent of the total chlorine was found.

It is therefore evident that potassium is very much more effective as a reducer than sodium, and is consequently better adapted for use upon such substances as the halogen substituted benzols, which belong to the most difficultly reducible class of organic halogen compounds. In the experience of the writer it gives, under the conditions out

= 1,

- 1.13

+ 0.37 +0.39 +0.39

THE heating effect due to the friction of the stirrer in the bomb calorimeter is generally supposed to be very small, but in connection with some calculations relative to the rate of radiation in the calorimeter certain discrepancies were found which could only be explained by the addition of considerable heat from the friction of the stirring apparatus, and a method for determining this heating effect was therefore evolved.

The object of this article is to show how the heat of friction, its magnitude under different conditions, and its relation to the calculation of the radiation correction may be accurately determined.

The rise in temperature during the initial period is due to the algebraic sum of the heat absorbed or evolved by radiation and the heat added by the stirring apparatus.

Let S = rate of rise in temperature due to radiation plus friction.

V = rate of rise in temperature due to radiation

alone.

F=S-rt1 = SI

The value of F is most accurately determined when one value of t is nearly zero and the other is several degrees above or below, or when one is positive and the other negative.

A number of sets of determinations for S and t, one of which is shown below for the purpose of illustration, were made on the calorimeter used in the Laboratory of the Consolidated Coal Co., Inc. The values for S were obtained by taking ten consecutive readings at intervals of one minute and averaging. The temperature of the calorimeter was then raised about 0.5° by means of a small ironwire coil, immersed directly in the water and heated electrically, and S was again determined in the same manner. In order to keep conditions as nearly uniform as possible, the calorimeter is surrounded by a water jacket, inch thick fitted over all. The stirrer is of the propeller a double lid placed over the top, and a felt covering one type, the shaft, to which is attached the pulley, projecting out from the top of the calorimeter. The results are given in Table I.

Ref. No. Average M'. 23.013°

0'0024°

TABLE I. Average M.

I.

18.544°

2.

22.987

19:065

3.

6.

22.928

21.046

8.

22943

21.987

Taking various combinations of S and t and calculating F, we get the results shown in Table II.

Thus F is found to be constant for almost any combination of S and t, provided the values for t are several degrees apart.

When F is calculated from the readings taken in an ordinary calorific determination the same result is obtained (see Table III.).

The water equivalent of the calorimeter from which these data were taken is 2944 grms., therefore the friction was adding to the apparatus 2944 X 0'00247'1 calories per minute. During the whole combustion period of six minutes this would be 6 x 7.1 = 42.6 calories.

The value for F obtained on another calorimeter which was equipped with the Mahler stirrer was o'005°. This instrument has a water equivalent of 2767 grms., which gives 13.8 calories per minute for friction or 82-8 calories for the whole combustion period.

This is much larger than would be suspected, but it is taken into account in the correction for radiation, as shown below. It emphasises, however, the necessity of having an absolutely uniform rate of stirring. The author found upon one occasion that even the loosening of the belt reduced the friction almost 50 per cent.

The best motor to employ is an alternating current induction fan motor. A direct current motor is not so desirable because changes in the voltage will also vary the speed. Stirring by hand should not be attempted if it is possible to obtain a motor, because experience has shown that it is impossible to stir continuously for twenty minutes and maintain a constant speed.

The relation of the friction to the correction for radiation may be shown as follows:

The formula used for the calculation of the radiation correction is that of Regnault-Pflaunder

rate of rise in temperature during the final period.

= mean temperature of the calorimeter during the initial period.

e' = mean temperature of the calorimeter during the final period.

01, 02... On

temperature at the end of the first, second... nth, minutes of the combustion period.

temperature at the moment of ignition.

In practice we do not get the values V and V', but V+ F and V' + F. If, then, these values be substituted in the formula in the place of V and V' we find that the value of C has been increased to that of C+nF. That is, we get the identical result which would be obtained if we used the true values of V and V' and then added to the value of C thus obtained the correction for the rise in temperature, F, caused by the friction during the combustion period.

THE following data have been gathered in an attempt to develope a means of distinguishing between gas oils derived from different fields. While it is manifestly impossible for an ordinary laboratory to attempt to separate and determine the constitution of the numerous hydrocarbons of gas oils, a simple method of determining the type of oil at hand would often be useful.

From several standpoints a method of identification of gas oils seems desirable. A great deal of the data on water-gas oil results is conflicting. This may possibly be due to a difference in composition of the oil used, a difference which could not be determined by ordinary tests. Some slight attempts have been made to determine the gas making properties of various gas oils by small scale experiments, but the most reliable information on the values of gas oils for gas making purposes is likely to be obtained from their actual use in water-gas practice. Data collected from actual practice require positive and simple methods of identification of the oil in use or a method adapted to the average gas works laboratory. Such a method would aid in the interpretation of results collected from various sources, tend to explain discrepancies, and render results reported in gallons per 1000 more intelligible.

Moreover, the most apparent application of a method of this kind is as an additional check on oil shipments. When water-gas results fall off unexpectedly, it becomes important to discover if there has been a change in the quality of the gas oils. Specific gravity tests and fractionations do not throw a great deal of light on the subject, but further tests are usually dispensed with, as they are expensive, tedious, and liable to be unsatisfactory. Luckily, to prove a change in the oil, it is not necessary to determine its constitution; any simple test serving to identify the oil is sufficient. It is proposed to use the bromine absorption number, which may be readily determined, for this purpose. Before proceeding to describe the process of bromination, it may be well to review briefly the chemical composition of petroleum.

Nature of Petroleum.

In defining petroleum, Mabery states.:-"Now, after years of hard labour, I have reached the conclusion that petroleum from whatever source is one and the same substance, capable of simple definition-a mixture in varying proportions of a few series of hydrocarbons, the product from any one field differing from any other field only in the proportion of these series and number of the series."

*Read at the Fourth Annual Meeting of the American Gas Institute From the Chemical Engineer, xi., No. 4.