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USAEA ltr, 31 Aug 1971

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IADIO'S7

EDGEWOOD ARSENAL

TECHNICAL REPORT

EATR 4054

COLORIMETRIC DETECTIONOF ALKYL ISOCYANIDES

by

Eleanor V. CrabtreeEdward J. Poziomek

Jaimary 1967

Physical Research Laboratory

Research Labonatorles

EDGEWOOD ARSENALEDGEWOOD ARSENAL, MARYLAND 21010

EDGEWOOD ARSENAL TECHNICAL REPORT

EATR 4054

COIJORIMETRIC DETECTION OF ALKYL ISOCYANIDES

by

lC,*loanor V. CrabtreelVdward .1. Piozionicek

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Physical Reeaeirch LaboratoryRetearch Laboratories

US ARMY EDGEWOOD ARSENAL

EDGEWOOD ARSENAL, MARYLAND 21010

FORE WOR{I)

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DIGEST

The subject of this research is the colorimetric- detection of alkylisocyanides. The objective was to develop a microchemical detection metondfor n-, sec-, and tert-butyl isocyanides.

Several aromatic amine-metal ion redox systems were investigatedfor the detection of alkyl isocyanides on filter paper or silica gel tubes.

It was concluded that microgram quantities of isocyanides may beeasily detected on filter paper or in silica gel tubes by using benzidine acetate-cupric acetate or p, p' -tetramethyldiaminodiphenylmethane (tetrabase)-cupricsulfate reagents. Interferences include those substances that are known tointerfere in the use of the same reagents for the detection of hydrogen cyanide.The lowest amount of n-, sec-, or tert-butyl isocyanide detectable is approxi-mately 0. 1 jig.

3

CONTENTS

L INTRODUCTION. 7

I, EXPERIM ENTATION .................................. 7.

A, Benzidlio A%.otate-Cupric Aceotatu Reagent .............. 7

B. Totrabase-Cupric Sulfate Reagent ........ 7

C. Spot Tests on Filter Papers ............................

]). Test Apparatus for Silica Gel Tubes. .............. 8

M. Techniques Involving Silica Gel Tubes ..............

F . leocyan d s ........................................... 10

II. IRESULTS. ...... . . . 10

A, Spot Tests on Filter Papers ............................ 10

1, Benzidlne Reagent ............................... 10

2. Tetrabase Reagent............... ............ 1

B. Tests In Silica Gel Tubes ................................ 1

WCA •N:vfe enc js...... ................................... 12

IV. DISCUSSION... . ............................................... 12

V. CONCLUSIONS ............ ........... ................ 13

LITERATURE CITED .................................... 15

DISTRIBUTION LL9T ......................................... .17

DD) FORM 1473 (DOCUMENT CONTROL DATA - R&D) .......... 31

5

I LIST OF FlOW RE.

Toat Appfti~ntu for SilicaftGeiTubeB...........*.*. 9

I IAST 01r TABLES

i Colorimnetric Detection of Butyl Isocyanidee In the VaporStato Using Silica Gel Tubes .................. * ......... I I

6

._I

COLORIMETRIC DE'FECTION OF ALKYL ISOCYANIDES

1hI. INTRODUCTION.

Recent surveys of a-addition reactions1 and synthesis methods 2

indicate considerable current interest in the use of isocyanides in organicchemistry. An isocyanide is usually detected by its characteristic and unpleas-ant odor. 2 Since olfaction is a sensitive and rapid method of identification, itis not surprising that only one chemical-detection method for isocyanide wasfound in the literature. Smith and Kalenda 3 mentioned that the color test ofPertusi and Gastaldi 4 is useful for detecting the presence cf isocyanides in

reaction mixtures, but gave no experimental details. This particular test isbased on the oxidation of benzidine to benzidine blue by cupric acetate when asuitable complexing agent is present. It is well known for its adaptation to thedetection of hydrogen cyanide. 5, 6 We studied several aromatic amine-metalion redox systems and will report in this paper the microchemical detection ofisocyanides on filter paper or silica gel tubes by using benzidine acetate-cupricacetate or p, p'-tetramethyldiaminodiphenylmethane (tetrabase)-cupric sulfatereagents.

II. EXPERIMENTATION.

A. Penzidine Acetate-Cupric Acetate Reagent.

This reagent, which will be called the benzidine reagent in theremainder of the text, was prepared from equal volumes of (1) 2.86 gm ofcupric acetate in a liter of water and (2) 675 ml of a solution of benzidine ace-tate (saturated at room temperature) and 525 ml of water. The solutions ofcupric acetate and benzidine acetate are best stored separately in well-stop-pered, dark bottles, and the reagent mixture should be freshly prepared eachtime it is used.

B. Tetrabase-Cupric Sulfate Reagent.

This reagent, which will be called the tetrabase reagent, was pre-pared by mixing equal volumes of (1) 100 mg of tetrabase and 500 mg of sali-cylic acid in 100 ml of acetone and (2) 1. 5 gm of cupric sulfate in 100 ml ofwate r.

7

The isocyanide test was initially developed as a spot test on filter

paper. Several kinds of papers were compared, since the sensitivit of certainspot tests can be increased severalfold with the proper filter paper.

A detector paper [a high a-cellulose-content paper tape impregnatedwith about 0. 87 Parez (American Cyanamid Co.) resin8 ] and several kinds of

S. S&S (Carl Schleicher & Schuell Co., Keene, New Hampshire) and Whatman(W. and R. Bolston, Ltd., Maidstone, England) papers were used.

D. Test.A aratus for Silica Gel Tubes,

A 2- by 9-cm test tube with a capacity of about 12 ml was fitted, bymeans of a 19/38 standard taper joint, with an adapter supporting a side-armair ialet and r. length of glass tubing that extended to within 5 to 10 mm of thebottom of the test tube (see the figurej. Silica gel tubes were connected by ashort length of rubber tubing to the upper end of the glass tubing. (The use ofsilica gel tubes for detection is well described in the open literature, repre-sented. here by Willianms and Miller, 9 Saltzman, 10 and Shepherd. 11) Vaporsfrorn the test tube were drawn through the detector tube by compressing arubber bulb.

E, Techniques Involving Silica Gel Tubes.

Samples of varying amounts of the pure isocyanides C ssolved inmethyleno chloride solution were measured with disposable microliter pipetsand placed in the test apparatus described above. When an unimpregnatedsilica gel detector tube is used, the isocyanide vapor is collected on the silicagel, 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 color is apositive test for iso<.yanide. A blue color is produced directly when the iso-cyanide vapor is sampled onto the silica gel tubes impregnated with tetrabasereagent. These detector tubes are prepared with the following reagentsimpregnated in silica gel: copper sulfate pentahydrate, p,p'-tetramethyl-diamninodiphenylmethane, and salicylic acid. IZ A red dye (coupled product ofdiazotized anthranilic acid with diethylaniline) is also added to mnask the bluecolor of copper sulfate.

RI-8l

E

Figure. Te~st Appairatus for Silica Gel Tubes

(A,Air ink; B, 2- by 9-cm test tube with 19/38 standard taper joint; C,

SA m

! ~ ~adapter'; D, silica gel tube, E, rubbci aspirator bulb with one-way valve) •

F. Isocyanides.

The n-, sec-, and tert-butyl isocyanides were synthesized byreacting tosyl chloride, quinoline, and the corresponding n-alkylforma-mide. 2, 13, 14

V A typical preparation of a test solution involved: (1) weighing"77. 1 mg of the chromatographically pure butyl isocyanide into a 10-ml volu-metric flask and diluting to volume with methylene chloride, (Z) preparing 1:50,1:100, and 1:250 methylene chloride dilutions of the stock solution, and (3) usingI - to 5 0-pLl aliquots of the diluted solutions as desired for testing.

III. RESULTS.

A. Spot Tests on Filter Papers.

1. Benzidine Reagent.

In each test, 10 gtl of the benzidine reagent was placed on the filterpaper, and 10 p.l of a methylene chloride solution containing 0. 18 pLg of n-butylisocanide was added. On the basis of the intensity of the blue color produced,the papers were grouped into three categories, as follows.

Most sensitive (positive test)

* Detecto'r paperS&S 589WWhatman 3

Intermediately sensitive (questionable test)

Whatman 120 S&S 597Whatman 31 S&S 604Whatman 5

Least sensitive (negative tesX)

Whatman 30 S&S 576Whatman 1 S&S 410Whatman 4 S&S 602Whatman 40 S&S 589 Blue ribbonWhatman 41 S&S 589 Black ribbonWhatman 2

10

2. Tetrabase Reagent.

The tetrabase reagent (10 p.I1 ) gave a pale blue color with 5 ýg ofn-butyl isocyanide on the detector paper (about the same intensity as 0. 5 kgof n-butyl isocyanide tested with the benzidine reagent). Similar results werefound with the Whatman 120 paper. The blue color with tetrabase reagent was Istable, whereas that with benzidine faded within a few minutes.

B. Tests in Silica Gel Tubes.

Sensitivity in iso'uyanide detection was improved by the use of silica§ gel detector tubes (see the table).

Table. Colorimetric Detection of Butyl Isocyanides

in the Vapor State Using Silica Gel Tubes

Technique Butyl isocyanides tested*n-Dutyl sec-Butyl tert-Butyl

Sampling through 0, 15 tg, definite 0.09 [g, definite 0. 1Z kg, definitesilica gel tubes light blue test testfollowed by - - I

ddtf AA... A4? na. AIC I O.AAy .. 41F 0 AQ Ilev '.nfI. - -m adito of b,,, -* C3r faint-lo

zidine reagent faded rapidly

Sampling through 0. 12 kg, definite 0. 09 kg, definite 0. 09 kg, definitesilica gel tubes blue color test testimpregnated withtetrabase reagent 0.06 - 0. 09 kg, 0.06 kg, faint 0.06 kg, faint

faint test

* The values are based on the assumption that all of the isocyanide placed inthe test apparatus was sampled.

c About 0. 1 kg of the butyl isocyanides was easily detected. Thecolor formed in 1he benzidine test faded rapidly after I to 5 mi. The bluecolor formed in tetrabase-impregnated tubes was stable; however, after pro-longed standing (about 2 hr), all the impregnated tubes, including the blankcontrols, turned dee' blue.

ii

C. Intterferences.

Substar.ces that interfere in the detection of hydrogen cyanide, otherthan hydrogen cyanile,itself, also interfere in the detection tests for isocya-nides. 5 These include volatile oxidizing or reducing agents and certain electro-

- philes or acids, For example, with the tetrabase reagent, we confirmed thatstrong acids give a yellow color and sulfides give a brown color,

IV. DISCUSSION.

The mechanisms of the colorimetric tests for alkyl isocyanides withthe benzidine or the tetrabase reagent are probably similar to those describedfor the well-known methods for cyanides. The benzidine test, sensitive to0. Z5 Vg of cyanide in a limit of dilution of 1 in z00,000, 5 is one of the easiestand most sensitive methodg for detecting cyanide. 6 This reaction (equation 1)takes place because the oxidation potential of Cu(II) salts is increased by theremoval of Cu(1) salts through the formation of insoluble cuprous complexes.

Cug) + HzN QQNHz + CU(I)+ ,HX (1)

bernidine ZN NHZ

benzidine blue

The colored oxidation product of tetrabase contains the quinoidal orcarbonium cation (equation 2). Only the salts of these cations are blue.

(CH 3)(2N)Z oi- (C(Ci3) )

+(-+ -0 -- H /(CH3))N(CH3)ZN4\ -Q 1-IOH N (C! 3)2

When they are exposed to ammonia vapors, the colorless carbinol base isformed; with the addition of acetic acid, the blue color reappears.

The benzidine test can be modified by the use of other anmines,such as o-tolidine, p-diarninodiphenylamaine, p-aminodimethylaniline, oro-dianis idine.

After this work had been terminated, Feigl and Anger 1 5 publisheda procedure for hydrogen cyanide and cyanogen in which the benzidine andcupric acetate were replaced by tetrabase and cupric ethyl acetoacetate. Thedetection limit was I jig of hydrogen cyanide. This reagent combination shouldalso be effective with the alkyl isocyanides, but it was not evaluated.

Although the tests reported in the present paper are subject to inter-ferences, they are very useful when combined with an independent mneasureementsuch as retention time in gas chromatography, Isocyanides are readily formedin the reaction of mono. N-substituted formamides with various electrophiles.We have developed a detection method for electrophiles by combining the io--cyanide test with the N- substituted formamide dehydration. Details arereported in a separate communication. *

V, CONCLUSIONS.

It was concluded that microgram quantities of isocyanides may be* easily detected on filter paper or in silica gel tubes by using benzidine acetate-

cupric acetate or tetrabase-cupric sulfate reagents. Interferences includethose substances that ave known to interfere in the use of the same reagentsfor the detection of hydrogen cyanide, The lowest amount of n-, sec-, or tertbbutyl isocyanide detectable is approximately 0. 1 Ig. , I 3

Sago

tI

* Poziomek, E. J., Crabtree, E, V., and Hoy, D. J. Unpublished data.

men, - 13

LITERATURE CITED

1. Ugi, I. Angew. Chiin, Intern, Ed. Engl. 1, 8 (1958).

Z. UgI, L, Fetzer, U., Eholzer, U., Knupper, H., andOffarinaun, K. Ibid. 4, 472 (19651).

13. Smith, P.A.S. , and Kalenda, N, W. J. Org. Chaen. 23,f • 1599 (1958).

4, Pertusi, C., and Gastaldi, E. Chem. Ztg. 37, 609 (1913).

5. Feigl, F, Spot Tests. Vol I, 4th ed. Elsevior PublishingCompany, New York, New York. 1954.

6. Bark, L. S., and Higson, H. G. Analyst 88, 751 (1963).

7. Poirier, R. H. , Wyant, ft E., and Harsh, Susan. SurfaceEffects on Limits of Visual Detection of Chromophoric Substances. In: Con-ference on Surface Effects in Detection, Bregman, J. I., and Dravnileks, A.,eds, Spartan Books, Inc., Washington, D. C. 1965.

8. Military Specification, MIL-P-51181 (MU), Detector Paper.US Government Printing Office. 4 March 1966.

- " 9. Williams, D. D., and Miller, R. R. Anal. Chean. 34, 225

(1962).-

10. Saltzn-an, B. E. Ain. Ind. Ilyg. Assoc, J. 23, 112 (196Z),

11. Shepherd, M. Anal. Chem,. 19, 77 (1947).

12, Military Specification. MII-S-50021A. Silica Gel, Impreg-nated; For Hydrogen Cyanide (AC) Detector Tubes. US Government PrintingOffice. 29 August 1960.

13, Casanova, J., jr., Schuoter, R. E., and jerner, N. D.J. Chem. Soc. 4280 (1963).

14. H-oy, D. J., and Pozioinek, E. J. CRDLR 3325. IsocyanideSynthesis. December 1965. UNCLASSIFIED Report.

15. Feigl, F., and Anger, V. Analyst 91, 280 (1966).

15s

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COLORIMIf-TRIC DETECTION OF ALKYL ISOGYANIDES

T DESCRIPTIVENOE (0T ype 7_7 of 1*oF&g I k tad M II -dV.da too)This work was started in September 1964 and completed in NovoenLbr 1964.

.0 AUTHOR(s) (tilast tn ,. "lita nameil, Initial)

Crabtree, Eleanor V., and Poziomek, Edward J.

i. np h 6A-F 15.?OTAL NO; OffPAGEO b. -No. qzý flciia=7 3a n a ry19 67 -

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I1- ABSTRACT

The subject of this research is the colorimetric detection of alkyl isocyanides.The objective was to develop a microchemical detection method for n-, see-, andtort-butyl isocyanides. Several aromatic anine-mnetal ion redox systemo woreinvestigated for the detection C alkyl isocyanides on filter paper or silica geltubes. It was concluded that microgram quantities of isocyanides may be easilydetected on filter paper or in silica gel tubes by using bonzidino acetate-cupricacetate or p, p' -tetr amethyldiaminodiphenylmnethane (tetrabase)-cupric sulfatereagents. Interferences include those substances that ara known to interfere inthe use of the same reagents for the detection of hydrogen cyanide, The lowestamount of n-, see-, or tert.butyl isocyanide detectable is approximately 0. 1 p.g.

S14. KEYWORDS

Isocyanides Tosyl chlorideIsonitrilea CyanidesBenzidine-Cu(U) reagent Silica gel tubesTetrabase-Cu(W) reagent Spot testsDetection ColorimetryElect rophiles butyl inocyanidesAlkylforu•amides

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