Table 111.
Comparison of Methods for Determination of Chloroform Based on Fujiwara Reaction
Temp.
Pyridine added, ml. 2 drops
Author and medium Feigl (3) 2 Fujiwara (P), body fluids 1 Cole ( I ) ,tissue extracts Gettler ( 6 ) ,tissue 5 extracts Daroga ( 2 ) , soil 20 and air Hildebrecht (6), 1 5
cc14
Milton ( 9 ) , urine 5 and blood Hunold ( 7 ) , air 10 Our method (8)
5
of NaOH reac- Heating Concn., tion, time, yo C. mm. X = mp M1. 1 drop 20 100 Few Visual 3 10 100 Just t o Visual boiling 20 100 2 1 Visual
Sensitivity, p.p.m. 20 1 1
10
20
100
1
Visual
10
10
20
100
5
525
30
10
100
3
525
10
5 drops
2.5
20
100
5
525
50
2
0.08 100
5
Filter S 49 Eko I1
10
10
CONCLUSION
It is obvious that the absorliance a t 366 nip is not due to the product that absorbs a t 530 mp, and that the compound that absorbs a t 366 mp is formed from the red compound, since the time necessary for attaining maximum absorbance in the ultraviolet is identical with that necessary for complete fading of the red color (Figure 2).
40
70
15
366
0.2
Using the conditions described under “Procedure,” a considerable increase in sensitivity over previous techniques for chloroform determination was obtained (Table 111). By measuring the absorbance after 4 hours, the sensitivity may be increased by a further 25%. Even by reading the absorbance a t 530 mp, as in previously reported procedures ($4,the sensitivity is increased. Figure 6 shows a comparison of
these three possibilities for determination of absorbance. Table I11 compares the methods used for the determination of chloroform in different media by different authors using the Fujiwara reaction. By changing the working conditions it would probably be possible to develop sensitive methods for other polyhalogen compounds. ACKNOWLEDGMENT
The authors thank Yona Burg for technical help in carrying out the experiments. LITERATURE CITED
(1) Cole, W. H., J. Biol. Chem. 71, 173 (1926). (2) Daroga, R. P., Pollard, A. G., J. Soc. Chem. Ind. 60, 218 (1941). (3) Feigl, “Spot Tests in Organic Analysis, 5th ed., p. 313, Elsevier, London, 1956. (4) Fujiwara, K., SiL. Nut. Ges. Rostock 6 , 33-43 (1916). (5) Gettler, A. S., Blume, H., Arch. Pathol. 11, 554 (1931). (6) Hildebrecht, Ch. D., ANAL. CHEW. 29, 1037 (1957). (7)Hunold, G. A., Schuhlein, R., Z.Anal. Chem. 179, 81 (1961). (8) Mantel, M., Molco, M., Stiller, M., Bull. Res. Council Israel 3, 10A (1961); Proc. of XXIXth Meeting, Israel
E.,
Chemical Society.
(9) Milton, R. R., Duffield, W. D., Lab. Practice 3, 318 (1954).
RECEIVED for review September 28, 1962. Accepted June 13, 1963.
Spectrophotometric Determination of Acetylenic Compounds as Mercuric Acetate Complexes SIDNEY SIGGIA’ and C. R. STAHL Central Research laboratory, General Aniline & Film Corp., Easton, Pa. A method is presented for determining monosubstituted and disubstituted acetylenic compounds via the triple bond on the molecule. The method is based on the formation of the mercuric acetate addition products of the acetylenic compounds and measurement of the ultraviolet absorption of these addition compounds. The method is selective for acetylenic compounds and is sensitive to low ranges of concentration.
T
EXISTING methods for determining acetylenic compounds are of three types: determination of unsaturation via the addition of bromine, hydrogen, or iodine halide (iodine number) (IS); determination of the acetylenic hydrogen in the case of monosubstituted acetylenes (HC-CR) HE
1740
0
ANALYTICAL CHEMISTRY
(1-6, 7-9, 1 3 ) ; and solvation of the acetylenic compound to the corresponding ketal or ketone and determination of the ketone (11, l a ) . The methods based on addition reactions lack specificity. Ethylenic compounds exhibit the same addition reactions and cause high results. Many organic compounds substitute bromine for hydrogen and oxidiaable compounds consume bromine. The same interferences occur to some extent with iodine halide methods. When the composition of the sample permits, bromination is a rapid and easy means for determining acetylenic compounds. Other reducible compounds interfere with hydrogenation methods by consuming hydrogen, and the methods are usually less precise than other methods for determining acetylenic compounds.
The methods for the determination of monosubstituted acetylenes by replacing the acetylenic hydrogen atom with a metal ion have a higher degree of selectivity than the methods involving addition reactions, but interferences still exist. These methods are either acidimetric or argentometric in nature. Thus, acids and bases in samples limit the use of the acidimetric methods, though in some cases the analysis can be accomplished by first neutralizing the sample. Compounds such as halides, mercaptans, cyanides, and others react with silver, limiting the use of the argentometric methods. These methods, of course, do not apply to disubstituted acetylenes ( R C r C R ’ ) since 1 Present address, O h hlathieson Chemical Corp., New Haven, Conn.
no replaceable hydrogen exists in these cases. Among the most specific methods for determining acetylenic compounds are those which involve reaction of the acetylenic triple bond with water (10, 11) or an alcohol (14) to produce a ketone or ketal, respec.tively 0 -
I L-+
OCHs CHaOH Hg +* BFn
Table I.
Results Obtained for Pure Acetylenic Compounds
Compound
Both the latter compounds are determined volumetrically with hydroxylamine hydrochloria e or, if acidimetry is impossible because of interferences, the carbonyl products can be measured gravimetrj cally with 2,P dinitrophenylhydrazine. Free carbonyl compounds in the sample constitute the only interference and these can be determined in a separate reaction and proper corrections can be applied. A method similar to the solvation approach exists (6) which involves reaction of the acetylenic group with mercuric acetate, but in this case the acetic acid liberated is titrated. The reaction between mercury compounds and the triple bond irs the intermediate step in the solvation of the acetylenic compound to a ketone. This method lacks precision and general applicability to acetylenic compounds, most probably because the mercury addition product does not remain as such but solvates to some degree to the corresponding ketal or ketone. Analytical methods utilizing solvation to the ketone or ketal lack sensitivity in the low ranges of acetylene content with one exc1:ption (10). This procedure is sensitive to very small amounts of certain acetylenes; however, some acetylenes containing other functional groups cannot be determined by this method. The 2,4-dinitrophenylhydrazones obtained are water soluble and do not extract into the cyclohexane layer. In the work with which the authors have been involved, the need became apparent for a method both selective for acetylenic compoimds and sensitive in the low ranges of concentration. In the ensuing investigations it developed that the mercury addition product generally absorbed n the ultraviolet region of the spectrum. Early attempts to utilize this approach were unsuccessful since water or altrohol were used as eolvents and the rdvation reaction which consumed the mercury addition intermediate proceeded a t too rapid a rate. It was then decided that acetic acid should be tried as the solvent, in which case the solvation should not be
Found
Wavelength, mr
Molar absorptivity
x
10-2
2-Prop yn-l-ol
4.8 4.8 4.8
4.7 4.7 4.7
3-Butyn-1-01
1.7 1.7 1.7
1.7 1.7
285
4.1
1.7
1-Hexyne
1 .o 1.9 1.9
1.9 1.8 1.8
295
6 .5
l-OctJyne
3.5 3.5 3.5
3.5 3.5 3.3
295
4.3
1-Dodecyne
4.0 4.0 4.0
4.0 4.0 4.0
295
4.7
2-Methyl-3-butyn-2-01
3.6 3.6 3.6
3.6 3.7 3.6
300
3.6
3-Octyn-1-01
1.1 1.1 1.1
1.2 1.1
320
31.8
1.2
Propargyl acetate
5.0 5.0 5.0
5.0 5.0 5.1
280
3.5
Dipropargyl ether
3.4 3.4 3.4
3.4 3.5
285
10.0
3.0 3.0 3.0
285
3.6
RC-CHnR' OCHs
Calcd.
hlg.
3.0 3.0
3.0
possible. The mercury addition product was found to be quite stable in this medium and the analysis was possible. The main advantage of the method described here is the ability to determine accurately and specificallysmall amounts of acetylenic compounds. However it should be added that for some acetylenic materials the absorption of the mercury addition product is such that it will permit precise assay (A1%) of high purity acetylenic compounds. The necessity of preparing standards is the one disadvantage of the method, but once a standard curve is obtained for a particular acetylenic compound, samples can be rapidly and easily analyzed. EXPERIMENTAL
Reagents. Mercuric acetate solution. Twenty grams of mercuric acetate were dissolved in 1 liter of acetic acid. Procedure for Standards. A solution of the acetylenic compound in acetic acid is prepared which contains 1 mg. per ml. Aliquots of this solution are pipetted into a series of 50ml. volumetric flasks and 25 ml. of mercuric acetate solution are added with a pipet to each flask. The solutions are diluted to 50 ml. with acetic acid and are allowed to stand at room temperature for 30 minutes. A blank
4.2
3.4
solution is prepared in the same manner except that the acetylenic compound is omitted. After 30 minutes the absorbances of the standards are determined at the proper wavelength against the blank with a Beckman Quartz Spectrophotometer or any other suitable instrument. One-centimeter cells are used for all measurements. A plot of absorbance us. milligrams of compound is prepared. Procedure for Samples. A sample which contains between 1 and 10 mg. of acetylenic compound is weighed into a 50-ml. volumetric flask, or, for samples which contain high concentrations of the acetylene, an aliquot of a n acetic acid solution of the sample may be used as in the procedure for the standards. Mercuric acetate reagent (25 ml.) is pipetted into the flask, and the solution is diluted to the mark with acetic acid. A reagent containing 20 grams of mercuric acetate in 1 liter of acetic acid was used except in the determination of low concentrations of certain acetylenic compounds in olefins. In these determinations, listed in Table I, a reagent solution containing 60 grams of mercuric acetate per liter of acetic acid was used. After 30 minut.es, the absorbance of the solution is determined a t the proper wavelength against the same blank as used for the standards. Milligrams of compound are read from the standard curve and per cent is calculated. VOL 35, NO. 11, OCTOBER 1963
1741
b
c
Table II.
Determination cf Acetylenes in the Presences of Ethylenes
Reagent concentration, gram.
Compound Acetylenic Ethylenic I-Octyne I-Decrne
WAVELENGTH ( m y )
1-lhdecyne
I-l)erene
1-Hexync
1-Pentene
2-Propyn-1-01
,411~1alcohol
1 ,-t-Butynediol
1,4-Butenediol
Figure 1. Spectra of acetylenic compounds in an acetic acid solution of mercuric acetate (a) 1-Dodecyne (b) 3-Butyn-1-01 (c) Dipropargyl ether
DISCUSSION AND RESULTS
Propargyl ac7etn t P
Allyl acetate
‘l’he method was tested on both monoand disubstituted acetylenic compounds. The spectra obtained for those compounds are presented in Figures 1 to 4. An examination of these curves will show that the complexes formed by mercuric acetate with certain acetylenic compounds have absorption spectra ivhich exhibit maxima, while those formed with other acetylenic compounds do not have definite maxima. When possible, the absorbance was measured at the maximum, but when no
1.0
11
Alkyne, % Added
0.12 0.73 5.75 0.19 1.13 8.68 0.12 0.72 5.80 0.20 0.60 2.91 2.91 4.76 0.29 0.40 0.40 0.Z 1.16 I .IS 5 30 5.30 0.10 0 60 4.76
Foucd 0.14 0.81 5.54 0.19 1.24 8.86 0.11
mercuric acetate per liter acetic
0.i9
5.80 0.16 0.60 2.91 2.51 4.67 0.26 0.34 0.37 0.68 0.59 1.00 4.74
4.74 0.06 0.40
acid 20 20 20 20 20 20 20 20 20 60 60 20 20 20 60 60 60 60 20 20 20 20 20
4.48
could be determined, but the method could not be used to determine certain disubstituted acetylenic compounds. Disubstituted acetylenic hydrocarbons (RC=CR’) compounds where R and R’ are alkyl groups) formed complexes which showed too small an increase in absorbance over that of the reagent to be determined. The complexes of 3hesyne and 3-octyne did not absorb
WAVELENGTH ( w y )
Figure 3. Spectra of acetylenic compounds in an acetic acid solution of mercuric acetate (a) Propargyl acetate (b) 2-Propyn-1-01
WAVELENGTH
(my)
Figure 2. Spectra of acetylenic compounds in an acetic acid solution of mercuric acetate [ a ) 2-Butyne-1,4-diol
(b) 1-Hexyne (E) 1-Octyne
1742
ANALYTICAL CHEMISTRY
definite maximurn was present in the spectrum of a complex, the absorbance was measured at the point of lemt slope. In general, the spectra obtained for the complexes of acetylenic hydrocarbons did not have definite maxima. Where the acetylenic compound contained a second functional group besides the triple bond, a maximum is usually exhibited by the spectrum of its mercuric acetate complex. All monosubstituted acetylenes tested
d A V E L E N G TH (mu,
Figure 4. Spectra of acetylenic compounds in an acetic acid solution of mercuric acetate ( a ) 2-Methyl-3-butyn-2-01
(b) 3-Octyn-1-01
sufficiently to be used for deterinining these compounds. In some cases no change in the absortlance of the reagent’ was noted on the addition of hydrocarbons of thi: type. Xo increase in absorbance of the mercuric acetate solution was caused by 3,6dimethyl-4-octyn-3,6-diol. In this particular instance, the absence of complex formation is probabl:? responsible for the failure of the method since it was previously observed ( 2 1 ) t.hat compounds of this type react very slowly with mercuric salts even a t elevated temperatures. With the exception of the above compound, all the disubstituted acetylenes t’ested which contained a second functional group other than the t,riple bond could be det’ermined by the method. Acetylenic compounds could be determined in the presance of ethylenic compounds in all case:; tested where the ratio of double bond to triple bond was not more than one hundred to one without change in the method. ’\J7here the ratio of double bcsnd to t.riple bond was greater than one :iundred to one, it was necessary to increase the concent,ration of the reagent from 20 grams of mercuric acetate per liter of acetic acid to 60 grams per liter in the deterniination of some compounds to obtain complete reaction of the triple bond. The concenlration of reagent used for determination of acetylenic compounds in the presence of ethylenic compounds is given in Table 11. Ethylenic conipounds in general appear to form complexes with mercuric acetate in acetic acid, but most of the complexes do not’ cause a n increase in absorbance. 2,4,4Trimethylpentene was the only olefin which was found to give an increase in
absorbance. A decrease in absorbance was noted in some cases when mercuric acetate complexed n ith ethylenic compounds, but except in the case of allyl acetate this decrease was not great enough in the region of measurement to cause serious errors. Low results were obtained for propargyl acetate in allyl acetate. The results obtained for acetylenic compounds alone are tabulated in Table 1 and those obtained for mixtures of ethylenes and acetylenes are given in Table 11. From Table I it can be seen that the number of milligrams of acetylenic compounds found by analysis was within one tenth of a milligram of that taken in all determinations. Therefore, the preciiion and accuracy of a determination should be within 1% if a 10-mg. sample i4 taken. The molar absorptivities of the complexes are included in Table I. The absorbances for all compounds tested except 3-octyn-1-01 remained the same from 30 to GO minutes. The absorbance of the 3-octyn-1-01 complex decreased continuously over the period of measurement, but the rate of decrease was slow enough that good results could be obtained. Compounds which absorb in the region of measurement, or form mercury complexs which absorb in this region, \\ill interfere with the method. With the exception of the olefin mentioned prel iously no interference has been encountered from mercury complexes. In most caqes in which sampler contain compounds which abborb in the ultra\ iolet region it is possible to eliminate the interference by using an acetic acid solution of the sample as a blank. The mercuric acetate causes only n small
increase in absorbance for which a correction can be applied. The quantity of mercuric acetate used in the above procedure begins absorbing at approximately 320 mp and the absorbance increases slowly to 280 mp. At 285 mw the absorbance is 0.05. Below 280 mp the absorbance increases rapidly. As much as 5 grams of water may be present without interference. The effect of higher concentrations was not investigated, but the production of ketone by hydration may cause a significant decrease in absorbance if the water concentration is too high, LITERATURE CITED
( I ) Altieri, ST. J., “Gaa Analysis and Testing of Gaseous Materials,” pp. 330-2, American Gas Association, Kew York. 184;. (2) Bakes, L., AIolinin, L. J.. A N A L . CHEV.27, 1025 (1955). (3) Chavastelon, ?*I., Conipt. Rend. 125, 245 (1597) ( 4 ) Gilbert, ‘T.W., Meyer, A. S IJliite, J. C.. As.zi,. CHEM.29. 1526 ilLh7.i. ( 5 ) He$zer, R.E., Ibzd.: 24, l b g i ( l 9 5 2 j . ( 6 ) Iioulkes, LI.> Bd1. Sot. C h i m Prai~ce 1953, -1-02. ( 7 ) l\lnrszak, I.,Iioulkes, )I., M e m . Serv. C‘him. Etat Puiis 36, Xo. 4, 421-6 ( 1951) . (8) Robey, R . F., Hudson, B. E., \l’iese, H. K., ASAI,.CIIEM.24, 1080 (1952). (9) Ross, W. H., Trumbuli, H. L., J . i l m . Chem. Sot. 41, l l S 0 (1919). (10) Scoggins, 121.W.>Price, H. A . , ASAI,. CREM.35, 48 (1963). (11) Siggia, S., Ibid., 28, 1351 (1956). (12) SiggjR, S., “Quantitative Organic Analyeis yi:t Functional Groups,” 2nd Kd., pp. 68-77, JViiey, S e n - York, 195A _I;_
(13) Siggia. S , Hanna, J. G., ANAL.CHEM. 21, 1469 (1949). (14) JYqner, C. D., Goldstein, T., Peters, E. I).> Ibzd , 19, 103 (1947). RscErvhn for review January 23, 1063. Accepted July 25, 1963
VOL. 35, NO. 11, OCTOBER 1963
1743
