Colorimetric Determination of Aliphatic Alpha-Nitrohydroxy Compounds LAWRENCE R. JONES and JOHN A. RIDDICK,
Research Department, Commercial Solvents Corp., Terre Haute, lnd.
A colorimetric procedure for the determination of a-
the slit width to give an absorbance reading of zero for the dilution containing no sample. Read the absorbance of each sample in a 1-em. cell. Plot absorbance against concentration using rectangular coordinate paper. Determination of a-Nitrohydroxy Compound Impurity in an a-Aminohydroxy Compound. Weigh about 10 grams of the aaminohydroxy compound into a 100-ml. volumetric flask. Dilute to volume with water and mix well. Transfer a IO-ml. aliquot to a 250-ml. round-bottomed flask. Add 10 grams of sodium bisulfite crystals, 10 ml. of 5.005 sodium hydroxide solution, and 55 to 60 ml. of water. Reflux for 30 minutes, then cool to 25' C. Transfer the contents quantitatively to a 100-ml. volumetric flask and dilute to volume with water. Prepare a blank by t r e a t ing 10 ml. of water in the round-bottomed flask with the same reagents as the sample. Transfer a 2.0-ml. aliquot to a Lewis-Benedict tube and treat in the same manner as the calibration standards.
nitrohydroxy compounds has been adapted to the determination of small amounts of nitro alcohols in amino alcohols. It is specific for the nitro alcohols in the absence of formaldehyde or other compounds that hydrolyze to formaldehyde in alkaline solution. The proposed method will quantitatively determine nitro alcohols in the range of 1 to 100 y with an accuracy within *2% and a precision within *l%.
B
OTH primary and secondary nitroparaffins condense with formaldehyde to form a-nitrohydroxy compounds. Catalytic reduction of a nitro alcohol produces the corresponding a-aminohydroxy compound. Completeness of reduction could be determined by a specific method for trace amounts of nitro alcohol a t this step. An aliphatic nitro alcohol determination per se is not reported in the literature. The methods reported by Grebber and Karabinos ( 8 ) , Jones and Riddick (IO), and Turba, Haul, and Uhlen ( 1 4 ) for secondary and tertiary nitro compounds are unsatisfactory for the determination of nitro alcohols. Nitro alcohols decompose in the presence of excess alkali into the starting materials: formaldehyde and nitroparaffin (9). Amino alcohols do not undergo this reaction. Chromotropic acid (1,8-dihydroxynaphthalene-3,6-disulfonicacid) forms a violet-colored complex with formaldehyde in a sulfuric acid medium ( 7 ) . This method utilizes the color intensity of the formaldehyde complex for the quantitative determination of the nitro alcohol content. The method may be used to determine 1 part of nitro alcohol in 1000 parts of an amino alcohol sample as well as both crude and purified samples of nitrohydroxy compounds.
EXPERIMENTAL
APPARATUS
The following is needed: a Beckman Model DU spectrophotometer, equipped with 1-em. Cores cells; Lewis-Benedict tubes (Corning No. 7860), graduated at 12.5 and 25.0 ml.; a cooling bath a t 25' C.; a steam bath; and refluxing apparatus. REAGEh-TS
2-Nitro-2-rnethyl-l-propanolJmelting point and clemental analysis t o indicate a purity of 99.9% or better. Prepare an aqueous standard t o contain 1 mg. per ml. of solution. Sulfuric Acid. Specificgravity 1.84, Mallinckrodt, low nitrogen. Chromotropic Acid Reagent. Prepare a 2% aqueous solution from the sodium salt of 1,8-dihydroxynaphthalene-3,6-disulfonic acid. Sodium Hydroxide Solution. Prepare aqueous O.5OAV and 5.00N solutions. Sodium Bisulfite Crystals. Merck, dried. PROCEDURE
Preparation of Calibration Curve. Transfer 0, 1.0, 3.0, 5.0, 7.0, and 10.0 ml. of the 2-nitro-2-methyl-1-propanol standard solution to six 100-ml. volumetric flasks and dilute to volume with water. These dilutions contain 0, 10, 30, 50, 70, and 100 y, respectively, of 2-nitro-2-methyl-1-propanol per ml. of solution. Transfer 1 ml. of a diluted standard to a Lewis-Benedict tube. Add 1 ml. of O.50N sodium hydroxide solution, mix, and place in the 25" C. cooling bath for 5 minutes. Add 1ml. of chromotropic acid reagent, dilute to 12.5 ml. with sulfuric acid, and mix well. Immerse the tube in the steam bath for 10 minutes. Remove and cool to 25' C. in the cooling bath. More acid may be added to bring the volume to 12.5 ml. Transfer the solution t o a I-cm. Corex cell. Set the spectrophotometer a t a wave length of 580 mp. Adjust 254
The method consists of the decomposition of the nitrohydroxy compound with alkali to formaldehyde, and the formation of a colored complex with the formaldehyde and chromotropic acid in strong sulfuric acid, The effect of variables upon the degradation of 2-nitro-2methyl-I-propanol to formaldehyde was investigated. These included the stoichiometry of the reaction, the strength of alkali required for decomposition, and the time and temperature needed for the release of formaldehyde. It was found that the normality of the alkali had no effect on the amount of formaldehyde released. Any excess of alkali waa adequate to decompose the nitro alcohol almost instantly at room temperature. A 1.0-ml. aliquot of a O.5OAV solution of sodium hydroxide and a &minute reaction time mere chosen to ensure complete degradation. Stoichiometry of Reaction. Samples of each nitro alcohol were analyzed by the method and calculated as formaldehyde, using formaldehyde BS a standard. In all cases the expected molecular ratio of formaldehyde was found. 2-h'itro-1-butanol and 2-nitro-2-methyl-1-propanol decompose to yield one molecule of formaldehyde each. 2-Sitro-2-methyl-I, 3-propanediol, 2-nitro-2-ethy1-1,3-propanediol,and tris(hydroxymethy1)nitromethane decompose to yield tm-o molecules of formaldehyde per one molecule of nitro alcohol. Formation of Color Complex. The variables encountered during the sulfuric acid condensation of formaldehyde and chromotropic acid have been adequately examined and reported (1-7, 11-13). APP LICAT1ONS
The five commercially available nitrohydrosy compounds mentioned above were quantitatively determined by the described method. It was possible to determine small amounts of each in the presence of the corresponding amino compound. The aminohydroxy compounds prepared by the reduction of the above nitro compounds are stable in alkali and do not release formaldehyde. However, the presence of aminohydroxy compounds does inhibit the color formation between chromotropic acid and the formaldehyde released by the nitrohydroxy impurity. The results obtained by the direct analysis of a sample of 2nitro-2-methyl-1-propanol ( N M P ) in the presence of large amounts of 2-amino-2-methyl-1-propanol (AMP) are illustrated in Table I. The amine present apparently either combined with the formaldehyde to form a Schiff's base, combined with chromotropic acid to the exclusion of the formaldehyde, or buffered the reaction
255
V O L U M E 28, NO. 2, F E B R U A R Y 1 9 5 6 Table I.
Effect of Amine on Determination
A M P Added, ?/RIl.
NXIP Bdded, y/hIl.
N M P Found, y/R.II.
5018.8 5018.8 1003.0 1003.0
50 100 50 100
5 14 35
LITERATURE CITED
77
Table 11. Determination of 2-Nitro-2-methyl-1-propanol in 2-Amino-2-methyl-1-propanol Mixtures AMP Added, G .
NAIP Added, llg.
N M P Found, hlg.
0,5045 0.5045 0,5045
5.0
4,960, 5.005 1.005,1.000 0.500.0.495 9 , 9 6 0 , Q .980
1.0 0.5 10 0
0,5046
Replicate results of the determination of small amounts of 2-nitro-2-methyl-1-propanol in 2-amino-2-rnethyl-l-propano1, using the reflux modification, are given in Table 11.
Beyer, G . F., J . Assoc. Ofic. Agr. Chemists 34, 745 (1951). B O O S , R. E., ANAL. CHEY.20, 964 (1948). Boyd, M. J., and Logan, M. A , J . Bid. Chem. 146, 279 (1942). Bricker, C. E., and Johnson, H. R., IND.ENG.CHEY.,ANAL.E D . 17, 400 (1945). Bricker, C. E., and Roberts, K. H., ANAL. CHEIM.21, 1331 (1949).
Bricker, C. E., and Vail, W. .1.,Ibid., 22, 720 (1950). Eegriwe, E., 2 . anal. Chem. 110, 22 (1937). Grebber, K., and Karabinos, J . V., J . Research A'atZ. B u r . Standards 49, 163 (1952).
mixture to such an extent that all of the formaldehyde was not released. The formaldehyde may be conveniently separated from the interfering aminohydroxy compounds by refluxing in alkaline bisulfite solution, The formaldehyde released from the nitrohydroxy compounds complexes with bisulfite and the complex reacts quantitatively with the chromotropic acid.
Hass, H. B., and Riley, E. F., Chem. Reus. 32, 373 (1943). Jones, L. R., and Riddick, J. A , , ANAL.CHEM.24, 1533 (1952). Klienert, T . , and Srepel, E., Mikrochemie w r . Mikrochim. Acta 33, 328 (1948).
.\lacFayden, D. A., J . Biol. Chem. 158, 107 (1945). Speck, J . C., A N ~ LCHEJI. . 20, 647 (1948). Turba, F., Haul, R., and Uhlen, G.. Angew. Chem. 61, 73 (1949). RECEIVED for review September 29,
1955.
Sccepted November 14, 1955.
Determination of Total Nitrogen in Reformer Charge Stock R.
W. KING
and
W. B.
M. FAULCONER
Research and Development Department, Sun
Oil Co.,
A method is described for the determination of traces of combined nitrogen in reformer feed stocks that is particularly suitable for the concentration range from 1 to 100 p.p.m. It is a modification of a procedure originally described by ter Meulen, and involves conversion of nitrogen compounds to ammonia by catalytic hydrogenation and colorimetric determination of ammonia with Nessler's reagent. Application is limited to petroleum stocks having end points lower thanP.50' F. The sensitiFity is about 1 p.p.m. of nitrogen. Repeatability and accuracj are of the same order of magnitude as the sensitivity in the range below 20 p.p.m. The equipment is relatively inexpensi\e and simple to operate. An anal?sis may he completed in a little less than 2 hours.
D
U R I S G the past decade the petroleum industry has hecome increasingly av-are of the serious problems caused by nitrogen-containing compounds. The presence of even trace quantities of these materials may affect adversely the processing, storage, and quality of petroleum products. The presence of nitrogen compounds reduces the activity of cracking catalysts. It has been demonstrated that in catalytic charge stocks they seriously decrease the conversion to gasoline ( 7 , 6). Other catalysts, such as those used in reforming, polymerization, and isomerization, are susceptible to poisoning by nitrogen compounds (2). The increased commercial use of platinum catalysts for reforming straight-run naphthas has made necessary the determination of total nitrogen in such materials. The nitrogen content is generally in the range below 20 or 30 p.p.m. and therefore lies below the reliable detectability limits of the conventional Kjeldah1 and Dumas methods ( 4 ) . The low nitrogen content of these stocks makes a negligible reagent blank essential. This requirement may be most conveniently met by a catalytic hydrogenation technique in which organic nitrogen is quantitatively converted to ammonia. A method embodying this principle has
Norwood, Pa.
recently been described by Wankat and Gatsis (IO). il sample up to 1 liter in volume is hydrogenated a t high pressure using a nickel catalyst. The resulting ammonia is adsorbed on alumina pellets, the alumina neutralized, and the ammonia distilled into boric acid and titrated. They reported excellent results on a number of naphthas using this technique. However, the method is time-consuming and requires the use of a large capacity autoclave a t pressures up to 200 atm. with the attendant dangers of operation. I n 1924 ter Meulen (6) described a semimicroprocedure for the determination of nitrogen by destructive hydrogenation. The method is based on the fact that when 10 to 200 mg. of an organic compound containing nitrogen are pyrolyzed in a stream of hydiogen and the products are passed over a heated nickel catalyst, the nitrogen is quantitatively converted to ammonia, n hich may be absorbed and determined by customary procedures. The ter Meulen method has been generally accepted in Germany, but has received little attention in this country because of the short life of the catalyst. Recently Holowhak, Wear, and Baldeschnieler ( 3 )reported on the application of this method to petroleum frxtions. These authors n-ere able to develop an improved catalyst which v a s resistant to poisoning by sulfur or halogens. They s h o m d that the lower limit of detection \vas about 100 p.p.m., but suggested that by increasing the sensitivity of determining ammonia by spectrophotometry it might be possible to analyze accurately samples containing as little as 10 p.p.m. of nitrogen. I t seemed desirable to attempt to extend the ter LIeulen method to enable detection and estimation of concentrations as low as 1 p.p.m., as it is a more rapid and convenient method than a high pressure hydrogenation technique. The idea of developing more sensitive means of detecting the ammonia produced was abandoned in favor of one which would allow larger quantities of sample to be analyzed than in the conventional procedure. I n addition to increasing the sensitivity by producing larger quantities of ammonia, such an approach would eliminate the rather tedious handling of semimicro quantities of volatile materials If one attempts to pyrolyze samples much larger than about 300
