382
ANALYTICAL CHEMISTRY
until it is just pink. Cool the solution t o room temperature, and dilute to the mark. After thorough mixing, filter a portion of the solution through a rapid, fluted, 15-em. paper. Discard the first 5 ml. of the filtrate, then pipet 100 ml. into a 250-ml. Erlenmeyer flask. Add a drop of methyl red t o replace that adsorbed on the precipitate. Adjust the solution to the methyl red end point with 0.1 N sodium hydroxide. Read the buret, and continue as directed (3). Run a blank determination, which usually amounts to 0.10 to 0.20 ml.
Micro and semimicromodifications of the Kjeldahl procedure without distillation have been developed successfully for samples free from phosphorus (8). However, the distillation in the classical Kjeldahl micromethod is so rapid that no advantage is gained by eliminating it, and for this reason the microtechnique was not extended to samples containing phosphorus. ACKNOWLEDGMENT
The authors are grateful to the Research Council of Rutgers University for financial aid in this investigation.
RESULTS AND DISCUSSION
Table I shows the results obtained with pure organic compounds. Each entry in the third column is the mean of two determinations. Table I1 shows the results obtained with samples of dried blood. Each entry in the third column is the mean of two determinations. These tables show that the procedure is accurate and precise. The specified amount of zirconyl chloride is sufficient for samples containing 150 mg. of phosphorus. Should samples of greater phosphate ‘Ontent be encountered, the quantity Of zirconyl chlo- , ride should be increased proportionally.
LITERATURE CITED
(1) Hermann, R., J . prakt. Chem., 31,75 (1844). (2) Marcali, K., doctor’sthesis, Rutgers University, 1948. ENG.CIJEM..,ANAL.ED., (3) Marcali, K., and Rieman, W., 111,IND. 18, 709 (1946). (4) VenaMe, F. P., and Belden, A. W., J . Am. Chern. Soc., 20, 273 (1898). ’ RECEIVED August 16, 1947. Presented before the Division of Analytical CHEJ~ICAL and Micro Chemistry a t the 112th Meeting of the AMERICAN SOCIETY, New York, K. Y.
Preparation of Phosphomolybdic Acid from Phosphoric Acid and Molybdic Trioxide T.J. HASTINGS, JR.’, AND,H.A. FREDIANI Merck & Co. Inc., Rahway, ‘V.J .
T N T H E course of investigating methods for manufacturing phos1 photungstic and phosphomolybdic acids for analytical reagent use, irrespective of the relative amounts of phosphoric acid and molybdic trioxide initially employed the product obtained by the method suggested by Linz ( 5 ) was found to be the 1 to 12 acid. It has not been possible to prepare other ratios by this method, nor can the 1 to 12 acid be prepared in “reagent grade” quality by this process with a single recrystallization. Despite the chemical similarity betn-een tungsten and molybdenum, it has not been found possible in this laboratory to prepare the corresponding phosphotungstic acid by the mere interaction of phosphoric and tungstic acids in aqueous solution as suggested by Linz. The compound containing phosphorus and molybdenum was initially prepared by Debray ( 1 ) by the digestion with aqua regia of the yellow precipitate formed by the interaction of phosphoric acid and ammonium molybdate. Finkener, Pemberton, von der Pfordten, Gibbs, and Hundeshagen (9, 3, Q, 6, 7 ) showed that this compound had phosphorus and molybdenum present in a ratio of 1 to 12. All their methods of preparation were a t best vefy tedious and \Vu (8) Q-orkedout a synthesis in which sodium molybdate and phosphoric acid reacted in the presence of excess hydrochloric acid and the heteropoly acid n-as isolated from the reaction mixture by an ether extraction. In 1943, Linz (5) prepared the acid by the reaction of molybdic and phosphoric acids in aqueous solution. In view of the fact that Linz’s method uses water as the only solvent, it was thought to be a good one for the preparation of commercial quantities of the acid. The method is somewhat unsatisfactory because the product is contaminated with phosphoric acid after its crystallization from aqueous solution, but ether extraction yields the desired 1 to 12 acid. Even crystals of the acid so impure as to have an a p proximate 1 to 6 ratio (by analysis) yielded the 1 to 12 acid of high purity upon a single recrystallization from ether. EXPERIMENTAL
A. One mole (144 grams) of C.P. molybdic trioxide, l / 1 ~mole (9.6 grams) of C.P. 85% phosphoric acid, and 1500 ml. of water were heated to boiling in a Coors casserole. After 6 hours’ boiling ~
1
Present address, Rensselaer Polytechnic Institute, Troy, N. Y.
, the color changed from white to yellow and some molybdic triox-
ide remained undissolved. The residue was filtered onto a No. 52 Whatman paper and washed several times with water. The dried residue weighed 26 prams; 118 grams of molybdic trioxide had eone into solution. The vellow filtrate was evauorated in a Coors Zvaporating dish until crfstals appeared and then cooled to 25” C., whereupon the acid crystallized out in bulk. The phosphorus was determined as magnesium pyrophosphate and the molybdenum as lead molybdate. Duplicate analyses gave: 1 phosphorus t o 10.10 molybdenum and 1 phosphorus t o 10.12 molybdenum. The product (crystals) obtained mas dissolved in 200 ml. of n-ater and extracted with 300 ml. of U.S.P. ether i n a 1000-ml. separatory funnel. The remaining aqueous layer n-as extracted with ether in the presence of 5 ml. of concentrated hydrochloric acid to salt out the ether complex, and the remaining layer of mater was extracted again with ether. One hundred milliliters of water were then added t o the united ethereal extracts and crystallization of the aqueous solution in the presence of a little nitric acid yielded 129.2 grams of acid after refiioval of the ether. The analvsis gave a ratio of 1 phosphorus to 11.90 molybdenum and 1 phosphorus to 11.85 molybdenum. By calculation 118 grams of reacted niolybdic trioxide would give 131.7 grams of H7P (r\fO,O7)s.10HzO: this formula was calculated from the analytical data Therefore a 98’3 yield was obtained from the combined ethereal fractions. B. One mole (144 grams) of C.P. molybdic trioxide, 0.1 mole (11.5 grams) of C.P. 8570 phosphoric acid, and 1500 ml. of mater were maintained a t a boiling temperature for approximately 10 hours. ri residue of 16 grams of molybdic trioxide remained when the reaction mixture was filtered. Crystallization of the filtrate gave an acid having a ratio of 1 phosphorus to 8.68 molybdenum and 1 phosphorus to 8.80 molybdenum by analysis. By calculation 128 grams of reacted molybdic trioxide mould give a ratio of 1 phosphorus to 8.88 molybdenum. The impure phosphomolybdic acid obtained was purified by an ether extraction. Analysis of the acid gave a ratio of 1 phosphorus to 11.91 molFbdenum and 1 phosphorus t o 12.00 molybdenum. C. One mole (144 grams) of C.P. molybdic trioxide and 0.166 mole (19.2 grams) of C.P. 85% phosphoric acid were permitted t o react in the presence of 1500 ml. of water a t a boiling temperature for 6 hours. At the end of this time all the molybdic trioxide had dissolved. On evaporation a sirupy liquid was obtained which was difficult t o crystallize. Analysis of the solid product obtained gave 1 phosphorus to 5-62 molybdenum and 1 phosphorus to 6.68 molybdenum, Ether extrpction then yielded an acid with the following ratios: 1 phosphorus t o 11.85 molybdenum and 1 phosphorus to 11.95 molybdenum. D. One hundred and fifty grams of C.P. tungstic trioxide, 6.23 grams of C.P. 85% phosphoric acid, and 1500 ml. of water were maintained a t a boiling temperature for 12 hours. No reaction
V O L U M E 20, NO. 4, A P R I L 1 9 4 8
383
occurred. These are theoretical amounts of reactants to produce a phosphotungstic acid having a ratio of 1 phosphorus t o 12 tukgsten. Increasing the phosphoric acid concentration ten times did not make the reaction proceed. The authors have not had the opportunity of investigating t,he results obtained when freshly precipitated tungstic acid is used instead of the readily available trioxide.
( 2 ) Finkenel, Ii.,Ber., 11,1638 (1878).
(1) Debray, H., Compt. rend., 66,702 (1868).
R X C B I V E DOctober 1. 194ti.
LlTERATURE CITED
(3) Gibbs, W., Am. Chem. J . , 3,317,402 (1881-82). (4) Hundeshagen, F., 2.anal.Chem.,28, 141 (1889)
(5) Linz, A., IND. ENG.CHEM.,ANAL.ED.,15,459 i l Y 4 . i r . (6) Pemberton, H., Be?., 15,2635 (1882). (7) Pfordten, 0. F. von der, Ibid., 15, 1929 (1882) (8) Wu, Hsein. 6 .B i d . Chem.,43, 189 (19201.
Volumetric Determination of Free Sulfuric Acid in Crude Sulfonic Acids 0. H. DAWSON, Humble Oil and Refining Company, Baytowrt, Texas OIL-soluble sulfonic acids produced when petroleum oils are treated with strong sulfuric acid contain varying amounts of the free mineral acid which, upon neutralization with alkali, results in the contamination of the finished soap with inorganic salts (sodium sulfate). Hence a rapid method for the determination of the free mineral acid (sulfuric acid) content of sulfonated oil or crude sulfonic acids is needed for plant control as well as in laboratory investigations. A procedure for the determination of sulfuric acid in the presence of sulfonic acids as described by Burton and Robertshan (1) involves repeated extractions of the sample with sodium rhloride solution and gravimetric determination of the extracted sulfuric acid by precipitation as barium sulfate. Although fairly accurate, this method is subject t o the objection inherent in most gravimetric procedures-it is time-consuming. Uarron and Schifferli ( 2 ) have presented a method for the quantitative determination of the organic sulfonate content of synthetic detergents which may be used when the sulfuric acid content is not of prime importance. Laboratory studies have shown that the sulfuric acid contained in a mixture of sulfonic acids, oil, and water can be determined rapidly and with a fair degree of accuracy by water extraction (and titration) of the mineral acid from a n-amyl alcoholbenzene solution of the crude sulfonic acid sample. The sulfonic acid-oil mixtures encountered are soluble in the n-amyl alcoholtwnzene solution, and repeated extraction with water will remove all the mineral acid and only traces of the organic acids. Sulfonic acid-oil mixtures which contain impurities insoluble in n-amyl alcohol-benzene solution obviously cannot be analyzed conveniently by this method. PROCEDURE
Measure by means of a pipet exactly 10 ml. (or weigh 10 grams) of the sulfonic acid into a 125-ml. separatory funnel. Add 30 ml. of n-amyl alcohol and 60 ml. of benzene, and mix by shaking. Extract the solution with two or more successive 10-ml. portions of distilled water, allowing sufficient time (2 to 15 minutes)
Table I.
after each extraction for the water layer t o become clear before separating and proceeding with the next extraction. Titrate each water extract separately with standard 0.1 N or 0.05 iV alkali. Continue the extractions until an approximately constant titration value is obtained (three to four extractions). The major portion.of the sulfuric acid is always present in the first water extract, and a good, quick estimate of the mineral acid content can be obtained by titration of this first extract. The titer of the successive water extracts diminishes rapidly and becomes essentially constant after the second or third extraction. This constant residual value is due t o the extraction of traces of sulfonic acid after removal of the sulfuric acid has been completpd. RESULTS
Table I presents the data obtained when three different sulfonic acid samples are analyzed by the volumetric method described above. Data presented in Table I are calculated as follows: Sample Xo. Analysis No. T s (as grams per liter of sample) Tk (as grams per liter of sample) No. of titers averaged
s T
=
[Ts - Tk X
(lv
- 111
1 1
2
1
3
2 2
3
1 ' 2
3
12.59 11.61 32 84 32.73 32.54 10.02 10.45 10.71 0.30 0.18
0.26 0.19 0.15
0.10 0.11 0.17
4 6
3 6
2 5
4 6
3 6
2 6
11.09 10.71 31.54 31.78 31.79
2 5
2 5
9 62 10.01 10.03
Samples 1 and 2 were prepared by adding known amount,s of sulfuric acid to sulfuric acid-free sulfonic acids. Sample 3 (plant produced) contained an unknown amount of sulfuric acid and was evaluat'ed by the gravimetric method mentioned above ( 1 ) . These data indicate that in evaluating the sulfuric acid content. of sulfonic acid-oil mixtures, deviations from true values of no more than =t2% can be expected.
Evaluation of Sulfuric Acid in Sulfonic Acid Samples
Method employed Volumetric Sample KO. 1 2 Yolume of sample analyzed, nil. 10 10 HzS04 in sample, gram per liter 10 40 ?im Analysis KO. 1 2 1 2 3 Water used, ml. per extraction 20 10 20 10 8 2 HzSOa extracted, gram per liter First extraction 10.75 10.05 30.60 30.55 29.70 Second extraction 0.65 0.83 1.08 1.35 1.70 Third extraction 0.34 0.22 0.37 0.27 0.44 Fourth extraction 0.30 0.17 0.27 0.22 0.39 Fifth extraction 0.30 0.17 0.27 0.17 0.19 Sixth extraction 0.25 0.17 0.25 0.17 0.12 H~SO4found,gramperliter 11.09 10.71 31.54 31.78 31.79 Deviation from known amount present Gram per liter +0.19 -0.19 -0.26 +0.02 -0.01 +1.78 -1.78 -0.82 -0.06 -0.03 %
3 10 T-nLriown
1 0
2 5
d
9.00 0.65 0.17 0.13 0.07
8.76 1.13 0.34 0.12 0.10
9.32 0.61 0.44 0.17 0.17
9:62 1O:Ol
..
..
... ...
5
1O:O3
... ,..
Gravimetric 3 10 Unknown ~1 2
..
