Microdetermination of Chlorine and Bromine in Organic Compounds Sodium Fusion Method L. J . LOHR', T. E. BONSTEIN, AND L. J. FRAUENFELDER Central Research Laboratory, General Aniline & F i l m Corp., Easton, Pa. determining chlorine and bromine i n organic compounds, liquid or solid, is described. The compound is ilecomposed TTith molten sodium in a small nickel bomb, and the .odium halide formed is determined either gravimetrically or ~olumetrically. The method has been used to analyze stable i,hloro co;npounds such as carbon tetrachloride, hexachloroi,enzene, and hexachloroethane. -4volumetric analysis can be raarried out in about, 45 minutes with an accuracy of better than 2 parts per 100 parts. A higher degree of accuracy can be obtained if the sodium halide is determined gravimetrically. The stability of halogen containing compounds differs widely, :ind the ease of decomposition depends upon the halogen present :ind the structure of the compound. The extreme stability of fluorocarbons and chlorofluorocarbons is well recognized, and suitable methods of analysis have been developed, but little information has been published concerning the analysis of stable rhloro compounds except chloroparaffins. This paper is conrwned niainly with the analysis of chloro compounds which are tleconiposed incompletely by the classical methods and consecluently give low results. The method, however, is not' complex and ran be used to analyze any chloro or bromo compound. The stability of halocarbons normally falls into the follom-ing order: fluoro, chloro, bromo, and iodo, but if the compound conGists of elements other t,han carbon, hydrogen, and halogen, the qtability might be greatly changed. For example, fluorobenzoic wid is decomposed quantitatively by Parr bomb (8) oxidation, imt certain aliphatic compounds containing a terminal trichloromethyl group are not decomposed complet~ely. T o predict the ,tability of a research compound and choose the proper method of decomposition offers a challenge. -1s a result of a collaborative study of methods of analysis of I Bromo and chloro compounds, Steyermark and Faulkner (10) $tate that the Parr bomb method is not recommended. I t is probable that a t least part of the inaccuracy of this method is t-aused by incomplete decomposition because of inadequate heating of the bomb. I n this laboratory the Parr bomb method has heen used to analyze simple compounds, but difficulty has been experienced in the analysis of many polychloro aliphatics and xromatics. .41so as a result of this collaborative st'udy, the Carius (9) and the catalytic combustion methods ( 4 , 1 1 ) were 1,ecommended for the analysis of both bromo and chloro coniljounds. Excellent results have been obtained in this laboratory ijy the Catalytic combustion method. This method gives lOlT rcsults on stable, volatile polychloro paraffins and similar compounds because of incomplete cornbustion. The lime fusion :nethod of 3IacSevin and Baxley (6) conipletel\r decoml>oses (.ompounds Of this type but gives 1017 results on chlorosulfone milides, disulfone anilides, and other compounds of equal staljility. (The chlorosulfone and disulfone anilides have a chlorine ::tom attached to carbon alpha to sulfone group.) -4disadvantage of this method is that the lime adheres to the side of the bomb SO tightly that it is often difficult to renove quantitatively. The Carius met,hod gives an accurate analysis of easily decomposeJ chloro compounds, but prolonged heating of over 6 hours is required to decompose sulfoxides, sulfones, highly chlorinated aromatics, quinonoid dyes, and metal phthalocyanines ( 7 ) . The halide ion is usually determined gravimetrically, but recently IYhite and Kilpatrick ( 1 2 ) have extended this method to the volumetric determination of the bromide ion. The Carius method, ~ I C R O M E T N O L for ,
1 Present address, E. I. d u P o n t de Neinours 8- Co., Inc., Burnside Laborat o r y , Penns Grove, N. J.
although widely used, has not been adopted in some laboratories because it is a sealed tube method. In the last decade, potassium or sodium fusion has been used for decomposing extremely stable fluorocarbons and chlorofluorovarbons which could not be decomposed quantitatively by standard oxidation methods. Elving and Liggett ( 2 ) report excellent analysis of halocarbons by decomposing the compound with alkali metal a t 400" C., in a sealed glass tube and determining the resulting sodium halide. Halocarbons were analyzed similarly by Kimball and Tufts ( 5 ) , who decomposed the compound in 3 nickel bomb a t 450" C. Burger ( 1 ) decomposed organic conipounds with purified potassium and determined the halide ion volumetrically, but this method is concerned mainly with the analysis of sulfur and does not describe the halogen analysis in sufficient detail. Grodsky (5)analyze1 a few bromo and chloro compounds on a micro and semimicro scale by decompositioii with potassium in a sealed glass tube but experienced difficulty in the determination of both chloro and bromo compound,? containing other elements. Because the need existed in this laboratory for a micromethotl for determining halogen in all types of organic compounds, regardless of stability, composition, or volatility, the merits of the fusion method were investigated, and a bomb method was developed for determining bromine and chlorine. The method has given an excellent analysis of stable, volatile, polychloro aliphatic compounds such as carbon tetrachloride, polychloro aromatics such as polychloro benzene and polychloro naphthalene, and chlorinated dyestuffs and polymers. Other stable structures and linkages, cont'aining chlorine, which are decomposed quantitatively, are aliphatic compounds containing a terminal trichloromethyl group, sulfone anilides, disulfone anilides, quinones, naphthaquinones, anthraquinones, benzanthones, and metal phthalocyanines. The decomposit'ion is carried out in a small nickel bomb heated with a Fisher burner, and the resulting halide is determined either gravimetrically or volumetrically by the Volhard method. .4 volumetric determination can be carried out in less than 45 minutes v i t h an accuracy of better than 2 parts per 100 parts. -1higher degree of accuracy can be obtained if the sodium halide is determined gravimetrically. QPPAR4TU S
The bomb is a modification of the lime fusion bomb described by MacSevin and Baxley ( 6 ) . The body of the bomb consists of a hollow nickel cylinder, open a t one end, with dimensions shown in Figure 1. The threaded collar A i* niatk from a hexagonal .steel bar, and plug C is made of brass. -1gasket is placed betIveen the bomb and the The gasket is ma& from a piece of sheet nickel by forcing the plug dolm on the nickel sheet arhich is Placed betyeen the Plug and the bomb. The gasket is then cut out and filed Circular. The bomb is sealed by clamping the steel collar in a vise and tightening the brass plug with a wrench. I t is important that the gasket is smooth and lnalces an air tight seal. Each new bomb assembly should be tested for leaks by submerging in water the sealed bomb containing a small amount of dioxide escape. dry ice' REAGENTS
Nitric acid, C.P. Sodium sulfite, C.P. Ferric alum indicator, saturated solution of C.P. ferric animonium sulfate. Silver nitrate, approximately 0.1 N , and standardized 0.02 .I-. -4mmonium thiocyanate, standardized 0.01 N.
1115
1116
ANALYTICAL CHEMISTRY
Hydrogen peroxide, 30%, C.P. Ethyl alcohol, C.P. Sodium hydroxide, approximately 1.0 12'. Sodium shot, 6- to 8-mm. spheres in xylene, supplied by Pierce Chemical Co., Rockford, Ill. This sodium shot, which is uniform a n d practically free of chloride, is suitable for micro work.
Table I.
Analyses of Chloro and Bromo Compounds
Chloro Compounds Benzylisothiourea hydrochloride, CsHiiSzSCla o-Chlorobenzoic acid, CiHsOzCld
Calcd. Found 17.49 17.606 17.41 22.65
22.64b 22.536 22.515 22.52 22.57
Hexachloroethane, C2Clse Hexachlorobenzene, CsCla8
89,85 89.57 89.80 74.70 74,72 14.66 (4.76 74.43 Carbon tetrachloride, 92.19 92.14 CCII! 92.22 91.95 Tetrachloroanthraquinone 4 0 . 9 9 4 1 . 0 2 CirHaOzClah 41.00 Research compound 52.39 12.30 CsHsOiClsh s2.43
P 3 q
PART C BRASS
Figure 1.
PAR r D &/ma
Sodium Fusion Bomb
Sodium rather than potassium was chosen for this procedure because of the convenience of the form and the purity. No source of potassium was found which had a sufficiently low concentration of chloride ion for a microdetermination. PROCEDURE
The bomb is cleaned with distilled mater and acetone and is dried in a stream of air or over an electric hot plate. A sample which will give a titration of 3 to 4 ml. of 0.02 N silver nitrate, or a t least 5 mg. of silver chloride, is weighed into the bomb. Solid samples are placed in the bomb by means of a long-stemmed Lyeighing tube, and liquids are weighed in a small sealed-glass bulb. After the sample is placed in the bomb, two dry pellets of .odium are placed on the sample, and the bomb is sealed. The bomb is held almost horizontally by means of a small ring and heated to a red heat for a t least 10 minutes. Care should be taken during heating so that only the bottom inch of the bomb is heated to red heat. Solids which sublime should be heated slowly a t the beginning of the decomposition. After heating, the bomb is allowed to cool for several minutes. It is quenched in a stream of t a p water and washed with distilled water. The bomb is opened, and the gasket is removed. Any material adhering to the gasket is washed with distilled water into a 250-ml. beaker containing 30 ml. of a 50% solution ?f ethyl alcohol. After washing the outside of the bomb with distilled water, the bomb and contents are placed in the beaker containing the alcohol and washings from the gasket. A watch glass is placed over the beaker immediately to avoid loss due to spraying. After decomposition of the excess sodium, the solution is heated almost to boiling to remove the dissolved hydrogen. The solution is neutralized carefully n-ith concentrated nitric acid, using phenolphthalein as the indicator, and 5 to 10 drops in excess are added. The solution is heated for several minutes until the hydrogen sulfide, which is formed if the compound contains sulfur, is expelled. Any residual hydrogen sulfide can be detected by smell. Vigorous boiling or reduction in volume is not recommended. After removal of the hydrogen sulfide, the solution is neutralized with sodium hydroxide solution, using phenolphthalein as the indicator, and 2 to 3 ml. in excess is added. Acidification to remove the hydrogen sulfide may be omitted if the compound being analyzed is known to be free of sulfur. Two milliliters of 30% hydrogen peroxide is added to the hot alkaline solution, and the solution is heated until the oxygen is expelled. Oxidation is necessary to decompose metal cyanides or other complexes formed during the fusion. Incomplete decomposition of these interfering compounds causes high results because they also precipitate silver ion. Gravimetric Determination of the Halide. After heating with peroxide, the alkaline solution is vacuum filtered through a micro Neubauer crucible into a 100-ml. beaker to remove glass, if
DeviaC1 Linkage tion or Type 0 . 1 1 Ionic< 0.08 Monochloro aroinaticc
0.01 0.12 0.14 0.13 0.08 0.28 0.05 0.02 0 04 0.06 0 27 0.05 0.03 0.24 0.03 0.01
Polychloro aliphaticc Polychloro aroniaticc
Polychloro aliphaticv Polychloro aroinzticc Polychloro aromatic and aliphatic trichloromethyl groupc Polychloro aromaticc
0.09 0.04
Research compound. CqHs02C16h Research compound. C1aH;OzClaFs z
59.28
59.52
0.24
34 93
35 15 34 75
Research compound C8H102SClr 1 Research compound CioH1zCl?k Research compound, CiaH11Chl Research compound, CsH00i?iClsS>~
54.82
34.91
55.04 55.12 35.l o b
Polychloro aromatic containing trifluoromethyl groupc 0 . 2 2 Polychloro aromaticc 0.30 0 . 1 9 Dichloro aromaticQ
44.78
44.68
0.10
Trichloro aromatic0
42.06
41.88b 41.95
0.18 0.11
+search compound, C-H~OZSCIIS"
45.90
45,86
0.04 0 06
Research compound, CiIHzeSOzCln Research compound, Ci7HisCIzOzh
11.94
Polychloro aromaticC1 on carbon alpha t o sulfone groupc Polychloro aromatioCI on carbon alpha t o sulfone groupc Chloro aromaticc
Research compound, CsHsOaClKah Bromo Coinpounds Bromoacetanilide CsHaOXBrn Research compound, ClzHoOzSBrh Research compound, CIzH80zSBrzh Research compound, CaHeOzBnh Research compound. CsH302NBr20 Research compound, CnHmNaOSBra Research compound, CloHlsOaNzSnBrj
0 22 0 18
45.96
21.80
11.77b 0 . 1 7 12.04b 0 . 1 0 21.78b 0 . 0 2 21.77 0.03 21.87 0.07
14.86
14.76b
% Bromine Calcd. Found 37.33 37.185 37.496 37.39b 37.43 26.89 26.87 26.95b 42.50 42.56 42.17 6 4 . 9 9 65 18 64.61 52.42 52.67 18.07
Dichloro aromaticc
0.10 ~ tion 0.1: 0.16 0.06 0.10 0.02 0.06 0 06 0.33 0.19 0.38 0.25
Sodium salte ~
~
i Type
~
e
a
18.16 0.09 18.09b 0 . 0 2
e 21 60 0 07 0 21 21 32 21 45 0 08 Composition confirmed b y carbon, hydrogen, nitrogen, and sulfur analvsis. 5 Volumetric determination. C Solid. d Standard used in this laboratory for the past 9 years. Composition confirmed by carbon and hydrogen analysis. The chlorine content has been found t o be 22.5970 by t h e P a r r bomb method s n d 22.6670 b y catalytic combustion method. e Eastman Xodak technical grade. i Baker's C.P. grade redistilled. Center cut fraction analyzed. a Liauid. h Composition confirmed by carbon and hydrogen analysis. i Chlorine analyzed 35.02y0 b y t h e lime fusion method. T h e stability of a compound containing a -CFa group is decreased by other substituted groups such as OH. f Composition confirmed b y carbon, hydrogen, and nitrogen analysis. k Composition confirmed b y carbon and hydrogen analysis. Carbon, hydrogen. and chlorine total 100.01%. 2 Same a s k. Carbon hydrogen, and chlorine total 99.89%. m Cornnound contains'theoretical amount of sulfur. 12.04% chlorine vas f o u n d byrthe-Pa& bnes. Triazenes decompose and liberate nitrogen quantitativelj by the folloning reactions: H I €I
