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Microchemical detection of isocyanides
Short communications Talanta. 1967. Vol. 14. pp. 857 to 860.
Per,ginmn Press Ltd.
Microchemical
857
Printed in Northern Ireland
detection of isocyanides
(Received 2 February 1967. Accepted 13 March 1967) RECENT surveys on u-addition reactions’ and synthesis methods* indicate considerable interest in the use of isocyanides in organic chemistry. The characteristic and unpleasant odour of an iso-cyanide gives such a sensitive and rapid method of identification* it is not surprising that only one chemical detection method was found in the literature. Smith and Kalendaa mentioned that the colour test of Pertusi and Gastaldi’ is useful for detecting the presence of isocyanides in reaction mixtures but gave no experimental details. This particular test is based on the oxidation of benzidine to benzidine blue by copper(I1) acetate when a suitable complexing agent is present. It is well-known for its ion adaption to the detection of hydrogen cyanide. s,B We studied several aromatic amine-metal redox systems and report in this paper the microchemical detection of isocyanides on filter paper or in tubes of silica gel with benzidine acetate-copper(H) acetate or p,p’-tetramethyldiaminodiphenylmethane-copp-er(II) sulphate reagents.
EXPERIMENTAL Reagents Benzidine acetate-copper(ZZ) acetate reagent (benzidine reagent). Mix, just before use, equal volumes of (a) aqueous cupric acetate solution, 2.86 g/l and (b) 675 ml of benzidine acetate solution (saturated at room temperature) mixed with 525 ml of water. The stock solutions are best stored separately in well stonnered. dark bottles. Tetrabiie-copper(ZZ) sulphate reagent (tetrabase reagent). Mix equal volumes of solutions of (a) 100 mg of tetrabase (p,p’-tetramethyldiaminodiphenyhnethane) and 500 mg of salicylic acid in 100 ml of acetone and (b) 1.5 g of copper sulphate in 100 ml of water. Apparatus Silicagel tubes. A 2 x 9-cm test-tube with a capacity of about 12 ml was fitted, by means of a 19/38 standard taper joint, with an adapter supporting a side-arm air inlet and a length of glass tubing that extended to within 5 to 10 mm of the bottom of the test tube (Fig. 1). Silica gel tubes7-s were connected by a short length of rubber tubing to the upper end of the glass tubing. Vapours from the test-tube were drawn through the detector tube by compressing a rubber bulb. Procedure with silica gel tubes Samples of varying amounts of the pure isocyanides dissolved in methylene chloride (l-50 ~1, 040044002M) were measured with disposable pipettes and placed in the test apparatus described above. When an unimpregnated silica gel detector tube is used, the isocyanide vapour is collected on the silica gel, the detector tube is removed from the apparatus, and the silica gel is moistened with a drop of either reagent. The appearance of a blue colour is a positive test for isocyanide. A blue colour is produced directly when the isocyanide vapour is sampled by drawing it through a silica gel tube impregnated with tetrabase reagent. Such a detector tube is prepared from silica gel impregnated with copper(I1) sulphate pentahydrate, p,p’tetramethyldiaminodiphenylmethane and salicyclic acid.1° A red dye (diazotized anthranilic acid coupled with diethylaniline) is also added to mask the blue colour of the copper(I1). The n-butyl, s-butyl, and t-butyl isocyanides were synthesized by reacting tosyl chloride, quinoline and the corresponding n-alkyl formamide.** RESULTS Spot-tests on jilter papers The isocyanide test was initially developed as a spot-test on filter paper. Several kinds of paper were compared since the sensitivity of certain spot-tests can be increased by using the proper filter paper.la _ *Benzidine reagent. In each test, 10 ~1 of the benzidine reagent were placed on the filter paper, and 10 ~1 of methylene chloride containing 0.18 ,ug of n-butyl isocyanide were added. On the basis of the intensity of the blue colour produced the papers were grouped into three categories:
Short communications
858
FIG. L-Test apparatus. A-Air inlet; B-2 x g-cm test-tube with 19138 standard taper joint; C-adapter; D-silica gel tuba; &rubber aspirator bulb with one-way valve.
Most sensitive (positive test) Detector paper* S&St 589 Whatmans 3 I~g~~2msitivity
Whatmau 33. Whatman 5 S&S 597 S&S 604
(doubtful test)
Least sensitive (negative test)
Whatman 30 ~~~
1
Whatman 4 whaman 40 whatmim 41 Whatman 2 S&S 576 S&S 410 S&S 602
S&S 589 Blue ribbon S&S 589 Black ribbon
Tetrabase reagent. The tetrabase reagent (10 ~1) gave a pale blue colour with 5 pg of n-butyl isocyanide on the paper tape impregnated with Parez@ 607 resin (about the same intensity as that given by 05 pg of n-butyl isocyanide with the benzidine reagent). Similar results were found with the Whatman 120 paper. The blue colour with tetrabase reagent was stable, whereas that with benzidine faded within a few minutes.
+ A high a-cellulose-content paper impregnated with about O.SOA of Pare,@ (American Cyanamid Co.) resinl* t Carl Schleicher t Schuell Co., Keene, New Hampshire, U.S.A. # W. and R. Balston, Ltd., acetone, England.
Short communications
859
Tests on the silica gel tubes The sensitivity of isocyanide (Table I).
detection
was improved
by the use of silica gel detector
tubes
ISOCYANIDESINTTIE VAPOURSTATEWITHSILICAGELTUBES
TABLB~.~LORIMETRICDBTBCI~ONOF
Amountofisocyanidetested*
Technique
n-Butyl
s-Butyl
t-Butyl
Sampling through silica gel tubes followed by addition of benzidine reagent
0.15 peg, definite light blue 0*06-0*12 /4g, faded rapidly
0.09 pg, detinite test 0.06 pg, faint test
0.12 pg, definite test 0.09 rug, faint test
Sampling through silica gel tubes impregnated with tetrabase reagent
0.12 pg, deiinite blue c&our 006409 /Jg, faint test
0.09 pg, deiinite test @06 rg, faint test
049 pg, definite test 0.06 pg, faint test
* It is assumed that all of the isocyanide placed in the test apparatus was sampled. About 0.1 ,ug of the butyl isocyanides was easily detected. The colour formed in the benzidine test faded rapidly after l-5 min. The blue colour formed in tetrabase impregnated tubes was stable, but after prolonged standing (about 2 hr) all the impregnated tubes, including the blank controls, turned deep blue. Interferences Substances that interfere in the detection of hydrogen cyanide also interfere in the detection tests for isocyanides.6 They include volatile oxidizing or reducing agents and certain electrophiles or acids. For example, with the tetrabase reagent, we coniirmed that strong acids give a yellow colour and sulphides give a brown colour. DISCUSSION The mechanisms of the calorimetric tests for alkyl isocyanides with the benzidine or the tetrabase reagent are probably similar to those described for the well-known methods for cyanide. The benzidine test, sensitive to 0.25 rg of cyanide at a limit of dilution of 1 in 200,000,’ is one of the easiest and most sensitive methods for detecting cyanide. B This reaction, equation (l), takes place because the oxidation potential of copper is increased by the removal of copper(I) as an insoluble complex.
Cu(II) + HEN-Q-o-NH*
--f
C”(l) +
benzidine benzidine blue
(1)
The coloured oxidation product of tetrabase contains the quinoidal or carbonium cation, equation (2). Only the salts of these cations are blue, and
(CH,),N-@%-Q-NW,),
(CH&N-o-CH=o=&CH.), Cu(I1) H+ -C(CH3)~N-Q-&H-~-N(CH~)~
(2)
Short communications
860
when they are exposed to ammonia vapour the colourless carbinol base is formed; with the addition of acetic acid, the blue colour reappears. The benzidine test can be modifled by the use of other amines such as o-tolidine, p-diaminodiphenylamine, p-aminodimethylaniline, or o-dianisidine. After this work had been terminated, Feigl and Angeri published a procedure for hydrogen cyanide and cyanogen in which the benzidine and copper(I1) acetate were replaced by tetrabase and copper ethyl acetoacetate. The detection limit was 1 pg of hydrogen cyanide. This reagent combination should also be effective with the alkyl isocyanides, but it was not tested. E. V. C-TREE E. J. POZIOMEK D. J. HOY
Physical Research Laboratory Edpewood Arsenal %&yiand 21010, U.S.A.
Summa~-Microgram quantities of isocyanides may be easily detected onfilterpaper orin tubesofsilicagel byusingbenzidineacetate-copper(II) acetate orp,p’-tetramethyldiaminodiphenylmethane-copper(II) sulphate reagents. Interferences include those substances which are known to interfere in the use of the same reagents for the detection of hydrogen cyanide. The lowest amount of n-, s-, or t-butyl isocyanide detectable is approximately 0.1 pg. ZusammenfasstmR-Mikrogrammengen von Isonitrilen lassen sich auf Filtrierpapier oder in Kieselgehohrchen leicht nachweisen mit Benzidinacetat-Kupfer(II) acetat oder p,p’-Tetramethyldiaminodiphenylmethan-Kupfer(I1) sulfat als Reagentien. Es stiiren die Substanzen, die such beim Nachweis von Blausaure mit diesen Reagentien stiiren. Die kleinste nachweisbare Menge n-, s- oder t-Butylisonitril ist etwa 091 pg. R&m&-On peut aisement detecter des quantites de carbylamines de l’ordre du microgramme sur papier filtre ou dam des tubes en gel de silice en utilisant des reactifs a l’ac&ate de benzidine-a&ate de cuivre(II) ou au p,p’-tetram&hyldiaminodiphenyhn&hane-sulfate de cuivre(I1). Les interferences comprennent les substances qui sont connues-comme g&antes lors de l’kmploi des memes reactifs-pour la detection de l’acide cyanhydrique. La plus faible quantite de n-, sou t butylcarbylamine detectable est approximativement de 0,l /lg.
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
I. Ugi, Angew. Chem. Intern. Ed., 1962, 1,8. I. Ugi, U. Fe&r, U. Eholzer, H. Knupper and K. Offermann, ibid., 1965,4,472. P. A. S. Smith and N. W. Kalenda, J. Org. Chem., 1958,23,1599. C. Pertusi and E. Gastaldi, Chem. Ztg., 1913,37,609. F. Feigl, Spot Tests, 4th Ed., Vol. 1, p. 258. Elsevier, New York, 1954. L. S. Bark and H. G. H&son, Analyst, 1963, 88,751. D. D. Williams and R. R. Miller, Anal. Chem., 1962,34,225. B. E. Saltzman, Am. Znd. Hyg. Assoc. J., 1962, 23, 112. M. Shepherd, Anal. Chem., 1947,19,77. Military Speciiication. Silica Gel, Impregnated; For Hydrogen Cyanide (AC) Detector Tubes. U.S. Government Printing Office, MIl-S50021A. 29 August 1966. J. Casanova, Jr., R. E. Schuster and N. D. Jemer, J. Chem. Sot., 1963,428O. R. H. Poirier, R. E. Wyant and S. Harsh, Surface Effects on Limits of Visual Detection of Chromophoric Substances, in Conference on Surface Effects in Detection, (J. I. Bregman and A. Dravnieks, Eds.), p. 333. Spartan Books, Washington, 1965. Military Specification. Detector Paper. U.S. Government Printing Office, MIL-P-51181 (MU). 4 March 1966. F. Feigl and V. Anger, Analyst, 1966,91,280.
Per,ginmn Press Ltd.
Microchemical
857
Printed in Northern Ireland
detection of isocyanides
(Received 2 February 1967. Accepted 13 March 1967) RECENT surveys on u-addition reactions’ and synthesis methods* indicate considerable interest in the use of isocyanides in organic chemistry. The characteristic and unpleasant odour of an iso-cyanide gives such a sensitive and rapid method of identification* it is not surprising that only one chemical detection method was found in the literature. Smith and Kalendaa mentioned that the colour test of Pertusi and Gastaldi’ is useful for detecting the presence of isocyanides in reaction mixtures but gave no experimental details. This particular test is based on the oxidation of benzidine to benzidine blue by copper(I1) acetate when a suitable complexing agent is present. It is well-known for its ion adaption to the detection of hydrogen cyanide. s,B We studied several aromatic amine-metal redox systems and report in this paper the microchemical detection of isocyanides on filter paper or in tubes of silica gel with benzidine acetate-copper(H) acetate or p,p’-tetramethyldiaminodiphenylmethane-copp-er(II) sulphate reagents.
EXPERIMENTAL Reagents Benzidine acetate-copper(ZZ) acetate reagent (benzidine reagent). Mix, just before use, equal volumes of (a) aqueous cupric acetate solution, 2.86 g/l and (b) 675 ml of benzidine acetate solution (saturated at room temperature) mixed with 525 ml of water. The stock solutions are best stored separately in well stonnered. dark bottles. Tetrabiie-copper(ZZ) sulphate reagent (tetrabase reagent). Mix equal volumes of solutions of (a) 100 mg of tetrabase (p,p’-tetramethyldiaminodiphenyhnethane) and 500 mg of salicylic acid in 100 ml of acetone and (b) 1.5 g of copper sulphate in 100 ml of water. Apparatus Silicagel tubes. A 2 x 9-cm test-tube with a capacity of about 12 ml was fitted, by means of a 19/38 standard taper joint, with an adapter supporting a side-arm air inlet and a length of glass tubing that extended to within 5 to 10 mm of the bottom of the test tube (Fig. 1). Silica gel tubes7-s were connected by a short length of rubber tubing to the upper end of the glass tubing. Vapours from the test-tube were drawn through the detector tube by compressing a rubber bulb. Procedure with silica gel tubes Samples of varying amounts of the pure isocyanides dissolved in methylene chloride (l-50 ~1, 040044002M) were measured with disposable pipettes and placed in the test apparatus described above. When an unimpregnated silica gel detector tube is used, the isocyanide vapour is collected on the silica gel, the detector tube is removed from the apparatus, and the silica gel is moistened with a drop of either reagent. The appearance of a blue colour is a positive test for isocyanide. A blue colour is produced directly when the isocyanide vapour is sampled by drawing it through a silica gel tube impregnated with tetrabase reagent. Such a detector tube is prepared from silica gel impregnated with copper(I1) sulphate pentahydrate, p,p’tetramethyldiaminodiphenylmethane and salicyclic acid.1° A red dye (diazotized anthranilic acid coupled with diethylaniline) is also added to mask the blue colour of the copper(I1). The n-butyl, s-butyl, and t-butyl isocyanides were synthesized by reacting tosyl chloride, quinoline and the corresponding n-alkyl formamide.** RESULTS Spot-tests on jilter papers The isocyanide test was initially developed as a spot-test on filter paper. Several kinds of paper were compared since the sensitivity of certain spot-tests can be increased by using the proper filter paper.la _ *Benzidine reagent. In each test, 10 ~1 of the benzidine reagent were placed on the filter paper, and 10 ~1 of methylene chloride containing 0.18 ,ug of n-butyl isocyanide were added. On the basis of the intensity of the blue colour produced the papers were grouped into three categories:
Short communications
858
FIG. L-Test apparatus. A-Air inlet; B-2 x g-cm test-tube with 19138 standard taper joint; C-adapter; D-silica gel tuba; &rubber aspirator bulb with one-way valve.
Most sensitive (positive test) Detector paper* S&St 589 Whatmans 3 I~g~~2msitivity
Whatmau 33. Whatman 5 S&S 597 S&S 604
(doubtful test)
Least sensitive (negative test)
Whatman 30 ~~~
1
Whatman 4 whaman 40 whatmim 41 Whatman 2 S&S 576 S&S 410 S&S 602
S&S 589 Blue ribbon S&S 589 Black ribbon
Tetrabase reagent. The tetrabase reagent (10 ~1) gave a pale blue colour with 5 pg of n-butyl isocyanide on the paper tape impregnated with Parez@ 607 resin (about the same intensity as that given by 05 pg of n-butyl isocyanide with the benzidine reagent). Similar results were found with the Whatman 120 paper. The blue colour with tetrabase reagent was stable, whereas that with benzidine faded within a few minutes.
+ A high a-cellulose-content paper impregnated with about O.SOA of Pare,@ (American Cyanamid Co.) resinl* t Carl Schleicher t Schuell Co., Keene, New Hampshire, U.S.A. # W. and R. Balston, Ltd., acetone, England.
Short communications
859
Tests on the silica gel tubes The sensitivity of isocyanide (Table I).
detection
was improved
by the use of silica gel detector
tubes
ISOCYANIDESINTTIE VAPOURSTATEWITHSILICAGELTUBES
TABLB~.~LORIMETRICDBTBCI~ONOF
Amountofisocyanidetested*
Technique
n-Butyl
s-Butyl
t-Butyl
Sampling through silica gel tubes followed by addition of benzidine reagent
0.15 peg, definite light blue 0*06-0*12 /4g, faded rapidly
0.09 pg, detinite test 0.06 pg, faint test
0.12 pg, definite test 0.09 rug, faint test
Sampling through silica gel tubes impregnated with tetrabase reagent
0.12 pg, deiinite blue c&our 006409 /Jg, faint test
0.09 pg, deiinite test @06 rg, faint test
049 pg, definite test 0.06 pg, faint test
* It is assumed that all of the isocyanide placed in the test apparatus was sampled. About 0.1 ,ug of the butyl isocyanides was easily detected. The colour formed in the benzidine test faded rapidly after l-5 min. The blue colour formed in tetrabase impregnated tubes was stable, but after prolonged standing (about 2 hr) all the impregnated tubes, including the blank controls, turned deep blue. Interferences Substances that interfere in the detection of hydrogen cyanide also interfere in the detection tests for isocyanides.6 They include volatile oxidizing or reducing agents and certain electrophiles or acids. For example, with the tetrabase reagent, we coniirmed that strong acids give a yellow colour and sulphides give a brown colour. DISCUSSION The mechanisms of the calorimetric tests for alkyl isocyanides with the benzidine or the tetrabase reagent are probably similar to those described for the well-known methods for cyanide. The benzidine test, sensitive to 0.25 rg of cyanide at a limit of dilution of 1 in 200,000,’ is one of the easiest and most sensitive methods for detecting cyanide. B This reaction, equation (l), takes place because the oxidation potential of copper is increased by the removal of copper(I) as an insoluble complex.
Cu(II) + HEN-Q-o-NH*
--f
C”(l) +
benzidine benzidine blue
(1)
The coloured oxidation product of tetrabase contains the quinoidal or carbonium cation, equation (2). Only the salts of these cations are blue, and
(CH,),N-@%-Q-NW,),
(CH&N-o-CH=o=&CH.), Cu(I1) H+ -C(CH3)~N-Q-&H-~-N(CH~)~
(2)
Short communications
860
when they are exposed to ammonia vapour the colourless carbinol base is formed; with the addition of acetic acid, the blue colour reappears. The benzidine test can be modifled by the use of other amines such as o-tolidine, p-diaminodiphenylamine, p-aminodimethylaniline, or o-dianisidine. After this work had been terminated, Feigl and Angeri published a procedure for hydrogen cyanide and cyanogen in which the benzidine and copper(I1) acetate were replaced by tetrabase and copper ethyl acetoacetate. The detection limit was 1 pg of hydrogen cyanide. This reagent combination should also be effective with the alkyl isocyanides, but it was not tested. E. V. C-TREE E. J. POZIOMEK D. J. HOY
Physical Research Laboratory Edpewood Arsenal %&yiand 21010, U.S.A.
Summa~-Microgram quantities of isocyanides may be easily detected onfilterpaper orin tubesofsilicagel byusingbenzidineacetate-copper(II) acetate orp,p’-tetramethyldiaminodiphenylmethane-copper(II) sulphate reagents. Interferences include those substances which are known to interfere in the use of the same reagents for the detection of hydrogen cyanide. The lowest amount of n-, s-, or t-butyl isocyanide detectable is approximately 0.1 pg. ZusammenfasstmR-Mikrogrammengen von Isonitrilen lassen sich auf Filtrierpapier oder in Kieselgehohrchen leicht nachweisen mit Benzidinacetat-Kupfer(II) acetat oder p,p’-Tetramethyldiaminodiphenylmethan-Kupfer(I1) sulfat als Reagentien. Es stiiren die Substanzen, die such beim Nachweis von Blausaure mit diesen Reagentien stiiren. Die kleinste nachweisbare Menge n-, s- oder t-Butylisonitril ist etwa 091 pg. R&m&-On peut aisement detecter des quantites de carbylamines de l’ordre du microgramme sur papier filtre ou dam des tubes en gel de silice en utilisant des reactifs a l’ac&ate de benzidine-a&ate de cuivre(II) ou au p,p’-tetram&hyldiaminodiphenyhn&hane-sulfate de cuivre(I1). Les interferences comprennent les substances qui sont connues-comme g&antes lors de l’kmploi des memes reactifs-pour la detection de l’acide cyanhydrique. La plus faible quantite de n-, sou t butylcarbylamine detectable est approximativement de 0,l /lg.
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
I. Ugi, Angew. Chem. Intern. Ed., 1962, 1,8. I. Ugi, U. Fe&r, U. Eholzer, H. Knupper and K. Offermann, ibid., 1965,4,472. P. A. S. Smith and N. W. Kalenda, J. Org. Chem., 1958,23,1599. C. Pertusi and E. Gastaldi, Chem. Ztg., 1913,37,609. F. Feigl, Spot Tests, 4th Ed., Vol. 1, p. 258. Elsevier, New York, 1954. L. S. Bark and H. G. H&son, Analyst, 1963, 88,751. D. D. Williams and R. R. Miller, Anal. Chem., 1962,34,225. B. E. Saltzman, Am. Znd. Hyg. Assoc. J., 1962, 23, 112. M. Shepherd, Anal. Chem., 1947,19,77. Military Speciiication. Silica Gel, Impregnated; For Hydrogen Cyanide (AC) Detector Tubes. U.S. Government Printing Office, MIl-S50021A. 29 August 1966. J. Casanova, Jr., R. E. Schuster and N. D. Jemer, J. Chem. Sot., 1963,428O. R. H. Poirier, R. E. Wyant and S. Harsh, Surface Effects on Limits of Visual Detection of Chromophoric Substances, in Conference on Surface Effects in Detection, (J. I. Bregman and A. Dravnieks, Eds.), p. 333. Spartan Books, Washington, 1965. Military Specification. Detector Paper. U.S. Government Printing Office, MIL-P-51181 (MU). 4 March 1966. F. Feigl and V. Anger, Analyst, 1966,91,280.