Microdetermination of Boron in Organoboranes by Carius Oxidation DONALD G. SHAHEEN' and ROBERT S. BRAMAN2 Callery Chemical Co., Callery, Pa.
b A Carius oxidation method has been developed for the microdetermination of boron in organoborones. The boric acid formed is determined by potentiometric titration with standard base after the addition of mannitol. The standard deviation of the method is ho.3370 absolute. Sampling procedures are described for compounds which react violently upon contact with fuming nitric acid.
T
of Carius oxidation (2, 3) to the determination of boron and carbon in organoboron compounds has been reported (4, 6). Fuming nitric acid oxidation has been used in a semimicro Carius method for a number of years a t the Callery Chemical Co. ( 1 ) . A micromethod was sought for the determination of boron to permit analysis of small amounts of research samples. The toxicity and the high energy content of some of the boron hydride derivatives were additional reasons for seeking a microdetermination. HE APPLICATION
Teflon bore stopcock was employed in place of the glass stopcock supplied with the instrument with considerable improvement in prefision. A Sargent Micro Carius furnace, No. 5-36460, is connected in series with a Model TS60 SP-2 timer, available from Mine Safety Appliances Co., Pittsburgh, Pa. Borosilicate glass Carius tubes, 9 inches long, 13-mm. o.d., and 8-mm. i.d., are used. Sampling Procedure. Samples containing !;om 1 to 4 mg. of boron are taken for analysis. Solids are weighed in stoppered sample holders, Fisher Scientific Co. No. 21-042. This is placed in a Carius tube containing 0.35 ml. of red, fuming. nitric acid. T h e stopper need not be removed from the sample holder before sealing the tube as i t is loose enough to allow good contact between the sample and the hot acid vapors. Liquids are weighed in capillaries made from 20 X 100 mm. Kimax melting point capillaries. The sample capillaries are prepared by drawing out a fine tip on one end and bending the capillary 90" about 5 mm. from the other end. A piece of 7-mm. 0.d. capillary bore glass tubing about 35 mm.
EXPERIMENTAL ~
Apparatus. A simple vacuum system consisting of a vacuum pump, a liquid nitrogen trap, and a side a r m stopcock is used to pump off the nitric acid after completing the oxidation. The Carius tube is connected to the vacuum system by a short length of Tygon tubing. A hair dryer is used to speed removal of the acid. A Precision-Dow Recordomatic titrator is used t o perform the boron titrations. A special syringe buret was constructed for use with the titrator. In order to perform microtitrations, a 10-ml. Luer-Lok syringe is used with its plunger filled with mercury. A 12/2 metal socket joint silver-soldered to the base of a large bore hypodermic needle is used to connect the IO-ml. syringe to the titration assembly. Two special adapters were obtained from Precision Scientific Co. to complete the assembly, a syringe clamp and adapter for catalog No. 68889 feed pump. A three-way l Present address, Reaction Motors Division, Thiokol Chemical Corp., Denville, N. J. * Present address, Armour Research Foundation, Chicago, Ill.
Table
B( OH )a Sample 1 2 3 4
I.
Effect of Excess Acid on Boric Acid Recovery
Recovery, Treatment All acid removed AU acid removed Wet with acid Wet with acid
Table 11.
%
100.5 100.7 101.9 102.8
Microdetermination of Boron by the Carius Method
Compound Dimethylamineborane, ( CH&NHBHs Sodium tetraborate, NazB407 Decaborane, BloH14 Isopropylamineborane, CaHrNH2BHa Trimethylamineborane, ( CHa)sNBH3 Morpholineborane, C,H9NOBHs Chlorodecaborane, B1oH&l bis-Acetonitriledecaborane, BloH12(CH8CN), Research compound"
a
long is placed on top of the bent end of the sample capillary in the Carius tube to act as a plunger. The fuming nitric acid and the sample are frozen in liquid nitrogen after the tube has been sealed and the tip cooled. The tube is shaken so that the plunger strikes and breaks the capillary a t the bent end. The Carius tube is immediately placed in the oven. Oxidation. The samples are oxidized overnight in the Carius oven a t 440' C. This is the temperature indicated by the oven thermocouple and is the maximum temperature. T h e temperature a t the top and bottom of the oven may be as much as 100" C. lower. The oven is turned on and off automatically by a timer. Erratic, low results are obtained if the oven temperature is below about 350" C., and a large percentage of the Carius tubes explode if the temperature is over 460' C. Titration. Table I shows t h a t high results are obtained if the nitric acid is not removed before titration of the boric acid-mannitol complex. This may be a result of interference from weakly acidic oxides of nitrogen. The Carius tube may be heated with a hair dryer after most of the nitric acid has been pumped off, The final portion of acid is volatilized by heating for about 1 minute after the boric acid appears to be completely dry. No significant amount of boron is lost in this step even if the heating period is prolonged several minutes. When all the acid has been pumped off, the Carius tube is removed from the vacuum system and scratched with a file about 3 inches from the tip. The tube is carefully broken and the con-
Calcd. 18.36 21.50 88.46 14.83 14.83 10.72 69.02 53.46 58.68 52.94 56.12 74.97 70.10
Boron, yo Found 18.66 f 0 . 0 9 21.69 f 0 . 1 3 89.49 f 0 . 2 3 15.24 f 0 . 0 4 15.25 f 0 . 0 2 10 76 =! 0 . 0 2 69.74 f 0 . 3 3 53.17 d~ 0 . 0 2 58.54 & 0 . 4 5 52.34 k 0 . 3 5 56.63 f 0 . 3 6 74.60 & 0 . 3 3 69.75
Detns. 4 2 2 2 2 2 3 2 5 2 4 3 1
Exact composition of these research compounds is classified.
VOL. 33, NO. 7, JUNE 1961
893
tents are washed into a 150-ml. beaker containing 10 to 15 drops of dilute hydrochloric acid, 0 . W . The solution is boiled for 1 minute to remove carbon dioxide, cooled, and titrated. No appreciable amount of boric acid is lost if the boiling time is extended 2 or 3 minutes. Standard 0.03 to 0.04N carbonate-free sodium hydroxide is used for the titration. The end point is taken as the intersection of the p H us. volume curve with a parallel line midway betxeen two parallel tangents. When the strong acid has been neutralized, about 10 grams of mannitoI is added and the titration is completed. The final end point is determined graphically as described above. Table I1 shows results obtained on a variety of boron-containing compounds. These compounds were mostly research samples, but they were considered to be pure, a n acceptable assumption in most cases since the samples were recrystallized, sublimed, or run through some other purification step prior to analysis. The standard deviation is
Table 111.
Analysis of Phosphorus and Fluorine Compounds
(Carius tubes appeared to be etched after oxidation of samples containing fluorine) Boron, yo Compound Calcd. Found ( CnHo)J’BH3 5.01 3.26 (CdH$)aPB(CZHS)~
3.60
(C~L)~PBHJ BloH1,(NaF added)
3.92 88.46 8.52
1.88 3.96 4.46 2.87 147.98 120.08 10.16 12.01 ~~
=t0.33% absolute.’ A majority of the analyses were above the theoretical values indicating a possible bias in the method. This may be due to leaching of boron from the borosilicate glass Carius tubes during the oxidation. Fourteen analyses performed on a sample of HiCal, a boron-based high
energy fuel, averaged 62.56 & 0.35%. Eighteen macro Carius analyses of the fuel gave an average of 62.6% boron. Six boron analyses per day can be performed by one operator. Phosphorus and fluorine interfered in the determination of boron by this method. Table I11 shows results of boron analyses performed on samples containing these elements. LITERATURE CITED
(1) Callery Chemical Co., Callery, Pa., unpublished data, 1954. (2) Carius, L., Ann. 116, l(1860). ( 3 ) Xederl, J. B., Xiederl, V., “Organic Quantitative Microanalysis,” 2nd ed., pp. 151-7, Wiley, Kew York, 1942. ( 4 ) Schlesinger, H. I., Brown, H. C.. Horvitz, L., Bond, A. C., Tuck, L. D., Walker, A . O., J . Ana. Chem. SOC.75, 222 (1953). ( 5 ) Wartik, T., Schlesinger, H. I., Ibid., 75,835 (1953).
RECEIVED for review October 18, 1960. Accepted March 20, 1961.
Reduction of gem-Dinitro and Trinitro Compounds with Tita nium(III) ChIo rid e MAE I. FAUTH and GEORGE W. ROECKER Research and Development Department, U. S. Naval Propellant Plant, Indian Head, Md.
b The reduction of three classes of nitro compounds b y titanium(ll1) chloride has been investigated, to determine the feasibility of this reaction for assay of these materials. For the gem-dinitro compounds 2,2-dinitropropane and 4,4-dinitropentanoic acid, one nitro group, corresponding to six equivalents of titanium(lll), is reduced. For the compounds with three nitro groups on a terminal carbon, such as trinitromethane and 2,2,2-trinitroethanoIr two nitro groups are reduced, consuming 12 equivalents of titanium(ll1). For the aromatic compound 2,4,6-trinitromesitylene, the expected 18 equivalents are required. High results are obtained for 1,3,5-triazid0-2,4,6-trinitrobenzene, probably because of partial reduction of the azide groups. When the conditions of the reaction are controlled, reproducible results may b e obtained.
T
HE reaction of titanium(II1) chloride with aromatic nitro compounds is well known. For nitroparaffins and their derivatives Rodd (9) has proposed the following reaction:
RCN(N02)Z 4 ”,OH
+ RCH=NOH +
RCHzNH,
The purpose of this investigation was 894
ANALYTICAL CHEMISTRY
to determine to what extent gem-dinitro compounds and trinitro compounds which have all three nitro groups on the same carbon are reduced by titanium (111) chloride and whether suitable analytical methods for this type of compound could be devised using this reaction. The compounds used were 2,2-dinitropropane, 4,4-dinitropentanoic acid, trinitromethane, 2,2,2-trinitroethanol, 1,3,5-triazido-2,4,6-trinitrobenzene, and 2,4,6-trinitromesitylene. The techniques of handling titanium (111) solutions and their application to the determination of nitro grcups have been described by Kolthoff and Belcher (6)* Methods for the reduction of aromatic nitro compounds with titanium(II1) have been discussed by Becker and Shaefer ( I ) , who give extensive references to the literature. EXPERIMENTAL
Materials and Reagents. The four compounds not commercially available were supplied by the Organic Division and may be synthesized by the following routes. 4,4-Dinitropentanoic acid may be obtained by the method of Schechter and Zeldin (IO), which involves the
reaction of 1-1-dinitroethane uith potassium hydroxide to form the potassium salt, which reacts with methyl acrylate to yield methyl 4,4-dinitropentanoate. Hydrolysis of the methyl ester provides the 4,i-dinitropentanoic acid. Trinitromethane. A convenient preparation is that of Ficheroulle and GayLussac (S), based on the Oxidation of acetylene with nitric acid. 2,2,2-TrinitroethanoI was described by Marans and Zelinski (6) and its preparation investigated by Ficheroulle and Gay-Lussac (4). Both used the reaction of nitroform and paraformaldehyde. 1,3,5 - Triazido - 2,4,6 - trinitrobenzene. Preparation and properties have been summarized by Davis ( 2 ) . The material used was obtained by nitration of 1,3,5-trichlorobenzene, followed by treatment with sodium azide. 2,2-Dinitropropane. A sample was supplied by Commercial Solvents Corp. 2,4,6-Trinitromesitylene, Eastman White Label, was used. ElementaI analyses were obtained for all of the compounds (Table I). Titanium(II1) chloride (Lallotte Chemical Co.) was purchased as the 209& solution and a 0.2,V solution prepared by adding 100 ml. of 37% hydrochloric acid to 150 ml. of the 20Yo titanium(II1) chloride solution and diluting to 1 liter. After dilution to approximate volume, the stock solution is deoxygenated by
