Volumetric Determination of Primary and Secondary Nitroparaffins LAWRENCE R. JONES
and
JOHN A. RlDDlCK
Commercial Solvents Corp., Terre Haute, Ind.
to volume x i t h water. Store in an amber, glass-stoppered bottle. This solution is the 0.25N reagent (based on sodium hydroxide) for primary nitroparaffin analysis. Hypochlorite Reagent B. Place 80 & 0.1 grams of sodium hydroxide pellets in a 1-liter volumetric flask containing water. Cool, add approximately 145 ml. of Clorox solution, and dilute to volume with water. Store in an amber glass-stoppered bottle. This solution is the 2.0,V reagent (based on sodium hydroxide) for secondary nitroparaffin analysis. Kitroparaffin Standards. The preparation, .purification, and characterization of the purity of the following nitroparaffins have been described (10). Stromethane (KM), 99.99 mole 70. Kitroethane (NE), 99.9+ mole '$&. 1-Sitropropane (1-XP), 99.9+ mole 70. 1-Sitrobutane (1-NB), 99.96 mole %. 1-Sitro-2-methylpropane ( l-N-2MP), 99.82 mole %. The impurity present was determined to be 1-nitrobutane. 2-Nitropropane (2-NP), 99.99 mole 7c. 2-Sitrobutane (2-SB), 99.9+ mole G.
.4 rapid titrimetric method based on functional group analysis for the determination of individual primary or secondary mononitroparaffins depends upon the chlorination of the nitro compounds, using sodium hypochlorite in alkaline solution as the reagent. The excess reagent is determined by a standard iodometric method. The reagent consumed during chlorination is a measure of the nitro compound present when interfering compounds are absent. Because of differences in equivalent weights, the method cannot be used to analyze mixtures of several nitro compounds, a usual limitation of functional group analysis. Any compound that chlorinates in alkaline solution or is oxidized by the hypochlorite solution will interfere. The method has an accuracy within 3~0.1%and a precision within ItO.05 yo.
T
H E mass spectrometer is the most useful means for analyzing mixtures of the several mononitroparaffins (nitroalkanes). However, when only a single nitroparaffin is present, a simple procedure based on functional group analysis can be used. This paper presents a rapid titrimetric procedure for the determination of individual primary or secondary nitroparaffins. Published techniques for functional group analysis of these types of compounds include oxidation by chromic acid ( 2 ) ,modified Kjeldahl nitrogen determination (4,Q), reduction of the nitro group (6-8, l a ) , and, for nitromethane, potentiometric titration with sodium methylate using n-butylamine as the solvent (3). These procedures proved unsatisfactory for the routine determination of all primary and secondary nitroparaffins. The chlorination of primary and secondary nitroparaffins can be explained as an electrophilic mechanism. All hydrogen atoms on the carbon attached to the nitro group can be replaced with chlorine when controlled amounts of an alkaline chlorinating reagent are used (1, 6, 11). The stoichiometric reaction is illustrated using nitroethane as an example. CH3CH&'Or
+ 2NaC10
SaOH
CH3CCl802
PROCEDURE
Determination of a Primary Nitroparaffin. Weigh 0.6 to 0.7 gram of nitromethane or 1.2 to 1.4 grams of the higher primary nitroparaffins into a tared 250-ml. volumetric flask containing water. Dilute to volume with water and mix thoroughly until the nitroparaffins dissolve. Place 10 ml. of the dilution in an iodine flask containing 25 ml. of hypochlorite reagent A. Prepare a blank from 10 ml. of water and 25 ml. of reagent A. Stopper flasks and allow to Btand a t room temperatuie for 15 minutes. Cool the flasks in the ice bath. Add 15 ml. of acetic acid and 15 ml. of potassium iodide solution, mixing after each addition. Allow to stand 10 minutes in the ire bath and titrate with 0.1N sodium thiosulfate solution to the starch end point.
Table I.
Equivalent Weights of Nitroparaffins
S i t r o Compound Nitromethane Nitroethane Sitropropane
+ 2XaOH
2-Xitropropane 2-Nitrobutane
This reaction is the basis of the present analytical method. The excess chlorinating agent is determined by an iodometric method.
Molecular mt.
Chlorine8 Added
Equivalent wt.
1 1
44.547 51.560
61.042 75.068 89.094
~
~
89.094
103.120
Table 11. Determination of Nitroparaffins ( P e r cent by weight)
APPARATUS
Iodine flasks, 500-ml., glass-stoppered. Volumetric flasks, 250-ml., glass-stoppered, short necked, Sormax brand or equivalent. Pipets, 5-, lo-, 15-, and 25-m1., Sormax brand or equivalent. Buret, 50-ml., Normax brand or equivalent. Ice bath.
NJI
NE
I-NP
2-NP
1-NB
2-NB
1-6-2-1MP
99.97 99.98 99.98 99.97 99.96
99.98 99.97 99.98 99.89 99.98
100.04 99.99 99.99 100.02 99.98
100.02 100.02
99.97 100.01 99.98 99.99 99.97
99.98 100.00 99.97 99.98 100.02
99.96 99.94 99.95 99.96 99.96
99.98 99.98 99.97
REAGENTS
Glacial acetic acid, ACS reagent grade or equivalent. Potassium iodide solution, 20y0 aqueous solution. Sodium hypochlorite, Clorox, 5.257, by weight sodium hypochlorite. Sodium thiosulfate, 0.1N, standard solution. Sodium hydroxide, ACS reagent grade pellets or equivalent. Starch indicator, 0.5y0 aqueous suspension. Hypochlorite Reagent A. Place 10 & 0.1 grams of sodium hydroxide pellets in a 1-liter volumetric flask containing water. Cool, add approximately 145 ml. of Clorox solution, and dilute
Determination of a Secondary Nitroparaffin. Weigh 1.2 to 1.4 grams of a secondary nitroparaffin into a tared 250-ml. volumetric flask containing water. Dilute to volume with water and mix thoroughly until the nitroparaffin dissolves. Analyze a 10-ml. aliquot of this solution as for primary nitroparaffins, but substitute hypochlorite reagent B for reagent A. Calculations.
1137
1138
ANALYTICAL CHEMISTRY Table 111. Effect of Alkali on Analysis of Nitroparaffins
Xitroparaffins Primary Kitromethane Nitroethane I-Xitropropane 1-Nitrobutane 1-Nitro-2-methylpropane Secondary 2-Nitropropane %Nitrobutane
0.00
99.99 102.30 99.18 99.23 99.88 13.81 9.20
(Per cent b y weight) Soriiialities of Reagents 0.05 0.10 0.23 050 1.00
2.00
3.00
90.57 95.86 97.06 99.11 99.02
84.91 91.63 94.02 98.79 98.81
109.95 103.99 102.55 101.28 100.19 99.99 105.78 104.11 103.50 102.01 100.78 99.98
99.99 100.01
100.02 100.01 100.00 99.97 100.03 99.99 100.04 100.04 99.94 99.94
where
B T N W
V
= = = = =
ml. of thiosulfate required by blank ml. of thiosulfate required by sample normality of thiosulfate grams of sample ml. of aliquot
The equivalent weights of the seven nitroparaffins tested are tabulated in Table I. APPLICATIOR-
This method has been applied to the determination of the individual nitroparaffins as a criterion of purity and to process samples where a single nitroparaffin is present. It cannot be used in mixture of nitroparaffins because of the difference in equivalent weights. Results of replicate analyses on high purity nitroparaffins are given in Table 11. EXPERIMENTAL
The influence of several variables on the quantitative applications of this reaction was investigated, including the concentration of alkali, the time and temperature of the reaction, and the stability of the chlorinated compounds in the alkaline reaction mist ure,
Table IV.
Effect of Time on Chlorination" (Per cent b y weight)
Secondary Time, Min. 2-NP 2-IiB 5 99.87 99.82 99.14 99.78 99.99 100.00 10 99.98 99.98 100.02 99.98 15 99.99 99.98 99.99 99.98 30 100.02 100.04 100.04 100.00 45 99.99 99.98 100.02 99.98 100.02 60 99.98 a Primary compounds were analyzed in 0.25N reagent, secondary i n 2.00N. NE
Primary
1-NP
Concentration of Alkali. I t x a s found that the concentration of alkali vias critical, in the sense that the optimum concentration for the determination of primary nitroparaffins was not the optimum concentration for the secondary ones. The data on the effect of alkali, presented in Table 111, indicate that the primary nitroparaffins react quantitatively in the range of 0.10 to 0.50S alkali. Secondary compounds react quantitatively in the range of 2.00 to 3.00N alkali. A 0.25N solution was chosen for the primary and a 2.0OAVsolution for the secondary compound. The high results for the secondary nitroparaffins] 2-nitropropane and 2-nitrobutane, in the lower alkali normalities (Table 111) may be due to oxidation by the hypochlorite solution or to side reactions caused by structural differences. The chlorine derivatives of nitroethane, 2-nitropropane, and 2-nitrobutane are soluble in the reaction mixture. The other nitroparaffins precipitate after chlorination.
99.97 99.98 99.98 100 04 99.96
99.90 99.94 100.03 99.99 99.95
96.82 99.58 99.18 99.88 99.48
Time and Temperature of Reaction. The chlorination proceeds rapidly a t room temperature. -4study was made of the time needed for complete chlorination and of the effect, of additional time upon the reaction, since the nitroparaffins themselves are sensitive to alkali (Table IV). While the chlorination appears to be complete in 10 minutes, a 15-minute reaction time nas chosen t o ensure complete chlorination. Samples that were allowed to stand for 1 hour in the alkaline reaction mixture before acidification gave quantitative results (Tahle IV). The chlorinated nitroparaffins are ststble in the alkaline reaction mixture. DISCUSSION
A basic procedure is presented for the volumetric detei mination of any individual primary or secondary aliphatic mononitroparaffin. Tertiary nitro compounds do not react. Because of differences in equivalent weights, mixtures of primary or secondary compounds cannot be analyzed by this method, a usual limitation of functional group analysis. All cornpounds that chlorinate in alkaline solution, or consume chlorine by oxidation of the hypochlorite solution, interfere. To show the precision, accuracy, and stoichiometry of the chlorination reaction, the data presented have been necessarily limited to the analysis of high purity nitroparaffins. The purity values for 1-nitro-2-methylpropane given in Table I1 are slightly higher than the 99.82 mole % determined by Toops (IO). These high results are due to the presence of 1nitrobutane as an impurity, which, having the same equivalent weight, is calculated as 1-nitro-2-methylpropane. The data in Table 11,when compared to the cryoscopic purities, show a standard deviation of 0.023$7,. The 95% confidence limit for a single determination is ~ k 0 . 0 5 7 ~providing , precautions are taken to minimize loss of chlorine or iodine. ACKNOWLEDGMENT
The authors wish to thank Emory E. TOOPS, Jr., for the preparation, purification, and characterization of the purity of all the nitroparaffins used in this study. LITERATURE CITED
(1) Boyd, T., Ph.D. thesis, Purdue University, Lafayette, Ind., 1941. ( 2 , Friedemann, F., Z. ges. Schiess- IL. Sprengstofw. 24, 208 (1929). (3) Fritz, J. S.,Lisicki, S . AI., ANAL.CHEM.23, 589 (1951). (4) Harte. R. A., ISD.ENG.CHEM.,ASAL.ED.7, 432 (1935). (5) Hass, H. B., Strickland, B. R., U. 8. Patent 2,256,839 (Sept. 23, 1941). (6) KiFpaf,'d., Ber. 25, 1714 (1892). (7) AIulliken, S. P., Barker, E. R., Am. Chem. J . 21, 271 (1899). (8) Ponzio, G., Gam. chim. ital. 33, I, 412 (1903). (9) Simek, B. G., Chem. Listy 25, 322 (1931). (10) Toops, E. E., J . Phys. Chem. 60, 304 (1956). (11) Vanderbilt, B. &I.,U. S.Patent 2,181,411 (Kov. 28, 1939). (12) Wallerius, G., Tek. Tidskr., U p p l . C (Kerni) 58, 33 (1928). RECEIVED for review February 29, 1956. Accepted April 18, 1956.
