Reaction of Nitric Oxide with Tri-n-butylborane - ACS Publications

18 Reaction of Nitric Oxide with Tri-n-butylborane MASAHIRO

Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 24, 2015 | http://pubs.acs.org Publication Date: January 1, 1964 | doi: 10.1021/ba-1964-0042.ch018

Ballistics

INATOME and LESTER P.

Research

Laboratories,

KUHN

Aberdeen

Proving

Ground,

Md.

Nitric oxide reacts with tri-n-butylborane at room temperature to yield three major product which are believed to be R NOBR (II), R BN(OR)NO (III), and R BNROBR (IV). Mild hydrolysis of IV yields R BOH and RNHOBR (I), which is a cyclic dimer. A mechanism proposed for the reaction involves the formation of a C-nitroso and a B-nitroso compound, which react with R B to yield II and IV, respectively. 2

2

2

2

2

2

2

3

s part of a continuing study of the chemistry of nitric oxide, an ir A teresting reaction between nitric oxide and tri-w-butylborane ha been discovered, which takes place at room temperature and give rise to some novel compounds containing boron, oxygen, and nitrogen In this paper we describe these products and suggest a mechanism for their formation. The reaction maybe carried out either by stirring tri-n-butylborane in an atmosphere of nitric oxide in a closed system, or by bubbling nitric oxide through the liquid tri-n-butylborane. In either case care must be taken to remove nitrogen dioxide from the nitric oxide and to exclude air from the system. The reaction is over when there is no further pressure change or gas absorption. The reaction was allowed to run for several hours longer to ensure its completion. Analysis of the gas after reaction in a closed system revealed that there were no major gaseous products and that 0 . 8 mole of nitric oxide reacted with 1 mole of tri-n-butylborane. Two minor gaseous products were 1 butene and n-butane, which were formed in yields of 0 . 0 8 and 0.02 mole per mole of borane, respectively. The crude reaction mixture was a pale yellow liquid, from whic no pure product could be obtained by careful fractional distillation. Gas chromatography was also ineffective, because decomposition occurred under the conditions required to pass the material through the column. Evidence for the structure of the reaction products had to be obtained from subsequent chemical reactions of the original reaction product. The infrared spectrum (cell = 0 . 1 mm.) of the crude reaction mixture contained no bands at frequencies above 1500 cm. except for the saturated C - H bands, indicating the absence of significant amounts of hydroxyl- or carbonyl-containing substances. -1

183

In Boron-Nitrogen Chemistry; Niedenzu, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1964.

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IN CHEMISTRY SERIES

Dilution of the crude reaction mixture with an equal volume of cold methanol resulted in the rapid precipitation of a white solid. Acid hydrolysis of this solid yielded di-n-butylborinic acid and JV-butylhydroxylamine. Reaction of di-n-butylborinic acid with JV-butylhydroxylamine resulted in the rapid formation of crystalline solid which, on the basis of elementary analysis, mode of formation, and hydrolysis, is probably ( N-n -butylamino-oxy)di-n -butylborane, R BONHR (I), where R = n-butyl. The similarity in the infrared spectra of the c r y s tals obtained from the reaction mixture and of the synthetic crystals indicates that the former is also I. Analysis, by infrared, of the crude liquid reaction mixture before the addition of methanol indicates that 0.08 mole of I was obtained from 1 mole of R B . Much more I must have been formed by a chemical reaction between its precursor and methanol which occurs rapidly in the cold. This is discussed further below. Acid hydrolysis of the crude reaction mixture yielded di-n -butyl borinic acid and N, AT-di-n-butylhydroxylamine. Esterification of d i n-butylborinic acid with N, N-di-n-butylhydroxylamine yielded a liquid product which on the basis of its elementary analysis, its mode of for mation, and hydrolysis, is probably (N, JNT-di-n-butylamino-oxy)di-nbutylborane, R B O N R (II). From the relevant infrared spectra it is clear that the crude reaction mixture contains a substantial amount of Π. After hydrolysis of 24 grams of the crude reaction product in aqu eous acid the mixture contained two layers—the upper organic layer and the lower aqueous layer in which the basic hydrolysis products (6 grams) were soluble. Analysis of the basic hydrolysis products by vapor-phase chromatography showed that mono- and dibutylhydroxylamine were formed in the molar ratio of approximately 2 to 1 and that no other amines were present in significant amount. Steam distilla tion of the organic layer under nitrogen yielded two fractions. The more volatile fraction was di-n-butylborinic acid (14 grams), identified by its infrared spectrum and by conversion to a solid derivative with 8-quinolinol (3). No significant amount of boronic acid was found, indicating that the borane is oxidized only to the borinate level of oxi dation by nitric oxide. The less volatile fraction (4 grams) of the steam distillate was redistilled at reduced pressure through a spinning band column to yield a substance whose analysis and molecular weight indicate the empirical formula R B(NO) (ΙΠ). The structure of this compound is discussed further below. Comparison of the infrared spectrum of ΙΠ with that of the crude reaction product indicates that m is a major reaction product. Enough information to deduce the structure of the substance which yields R BONHR upon treatment with cold methanol is now at hand. The analytical data obtained in the hydrolysis experiments show a fairly good material balance for the sum of the two reactions: the r e action of tri-n-butylborane with nitric oxide followed by acid hydroly sis.


2

3

2

2

3

2

2

H 0 2

R B + 0.8 NO 3

• O . 13 R B(NO) + 0.15 R N O B R 3

2

2

2

+ IV

- 0 . 3 RNHOH

+0.15 R N O H +0.8 R B O H + 0.13 R B(NO) 2

2

3


2

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Nitric Oxide and Tributylborane

185

Since, in the initial reaction mixture before hydrolysis, R N O H is present as R N O B R and no free R B O H is present, the substance (IV) which gives rise toRNHOBR on treatment with methanol must contain approximately (0.8-0.15)/0. 3 or 2 boron atoms per nitrogen atom and must give rise to 2 moles of dibutylborinic acid upon acid hydrolysis. We formulate this substance as R BNROBR (IV). Further evidence for the presence of easily hydrolyzable IV was obtained by shaking a dilute solution of the crude reaction mixture in CCl^ under nitrogen for a few moments with water and then drying. This treatment r e sulted in the appearance of a very strong infrared band at 3627 c m . " , which is the O - H band of dialkylborinic acids in C C ^ solution, and a somewhat weaker band at 3200 cm. " , which is the N-H band of RNHOBR . A similar experiment with a dilute solution of R BONR2 also produced the band at 3627 cm. but of much lower intensity, showing that IV is much more readily hydrolyzable than Π. The rapid solvolysis of IV is represented by the equation 2

2

2

2

2

2

2


1

x

2

2

- 1

R BNROBR 2

2

+ R'OH

•R BOR 2

î

+ RNHOBR2

where R' is H or methyl. The reaction between tri-n-butylborane and nitric oxide can thus be represented by the equation R B +0.8 NO 3

•0.13R B(NO) 3

2

+ 0.15 R B O N R 2

2

+ 0.3R BNROBR2 2

which accounts for all of the major products. Experimental Addition of Nitric Oxide to Tri-n-butylborane. Nitric oxide, after passing through a column of Ascarite (sodium hydroxide on asbestos, Arthur H. Thomas Co., Philadelphia, Pa.), and a bubbler, was led into 120 grams of tri-n-butylborane (Callery Chemical C o . , Callery, Pa.) contained in a three-necked flask equipped with a magnetic stirrer. The exit gases were passed through a bubbler and then through sodium hydroxide traps. The flask was cooled in a pan of water. The reaction is completed in. two or three days, depending on the rate of stirring. The weight of the liquid after the reaction was approximately 127 grams. The same reaction was carried out on a smaller scale in a 52-ml. vacuum line. Tri-n-butylborane (1. 35 grams, 7.4 mmoles) was placed in a 333-ml. flask, which was attached to the line. The small amount of gas dissolved in the liquid was pumped off and NO was admitted. The organoborane absorbed 5.9 mmoles of NO and evolved 0.15 mmole of 1-butene. η-Butane and 1-butene were determined by gas chroma tography, using a dimethylsulf olone column. (n-Butylamino-oxy)di-n-butylborane (I). An equal volume of meth anol was added to 127 grams of the cooled reaction mixture. White crystals, which formed, were filtered. The filtrate was repeatedly cooled and filtered in order to obtain additional product. The yield after crystallization from petroleum ether (b. p. 40-60° C.) ranged In Boron-Nitrogen Chemistry; Niedenzu, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1964.

186

A D V A N C E S IN CHEMISTRY SERIES

from 20 to 30 grams (m. p. 92-94° C ) . Elemental analysis suggested that the crystals are impure R BONHR. Calculated for C H j B N O : C, 66.36; N, 6. 57; H, 13.15; B,5.09. Found: C, 69.24; H,13.10;N, 6. 27; B, 5.40. Preparation of pure I is described below. The crystals (2 grams) were hydrolyzed with 50 ml. of 10% hydro chloric acid by refluxing the solution for 1 hour under nitrogen, yield ing 1 gram of a top layer. The top layer was treated with 1 gram of 8quinolinol dissolved in 24 m l . of 95% ethanol, a method used by Doug lass (3) for the preparation of solid derivatives of aralkylborinic acid. When the derivative did not precipitate out of solution, the solution was concentrated and cooled with dry ice. On cooling, crystals of the derivative came out of solution. The product was filtered (1.6 grams) and crystallized from cold 95% ethanol, yielding yellow crystals (m. p. 37-39°C). (All melting points and boiling points are uncorrected.) The extinction coefficient of the derivative in CC1 at 415 πιμ was 3100. Analysis. Calculated for C Η 2 4 B N O : C,75.85; H,8.98; B,4.02; N,5.2. Found: C, 75.62; H,9.24; B,4.37; N, 5.21. The hydrochloric acid solution was washed with ether to remove a small amount of w-butylboronic acid and made alkaline with concen trated sodium hydroxide solution under nitrogen, and a small amount of sodium diethyldithiocarbamate was added to prevent the decompo sition of iV-w-butylhydroxylamine formed (4). The alkaline solution was extracted with ether. The ethereal solution was dried and con centrated, yielding 0.86 gram of slightly wet N-w-butylhydroxylamine crystals. The crystals were dissolved in ether and treated with oxalic acid dissolved in ether to yield the crystalline oxalate. The oxalate was recrystallized from ethanol (m. p. 138-39°). Analysis. Calculated for C H N0 : C, 40. 21; H, 7. 3; N, 7. 7. Found: C,40.19; H,7.06; N, 7.54. Di-w-butylborinic acid (0. 74 gram) was added to 0. 75 gram of N-nbutylhydroxylamine under N and without the use of a solvent. White crystals formed around the flask and droplets of water were observed in the flask the following day. The crystals were washed with meth anol, yielding 1.04 grams of dried crystals. The crystals were r e crystallized from petroleum ether (m.p. 92-94°). Analysis. Calculated for C H B N O (213): C, 67.61; H, 13.28; B,5.07; N,6.57. Found: C,67.64; H,12.86; B,5.57; N,6.62. Molecu lar weight 404 (freezing point depression, benzene); 426, 403 (vapor pressure osomometer, manufactured by Mechrolab, Inc., 1062 Linda Vista Ave., Mountain View, Calif.). N, J^-Di-n-butylhydroxylamine. The crude reaction mixture (4.08 grams) was hydrolyzed with 50 ml. of 20% hydrochloric acid solution under N . The top layer (2. 58 grams) was treated with 8-quinolinol, yielding 2.85 grams of crude crystalline 8-quinolyl dibutylborinate. The hydrochloric acid solution was washed with ether and made alkaline under N , and sodium diethyldithiocarbamate was added. Crystals came out of the alkaline solution. They were filtered, washed with cold water, dissolved in ether, and dried over sodium sulfate. The ethereal solution was concentrated to obtain the N,N-di-n-butylhydroxylamine crystals. Yield: 0.17 gram; [m.p. 51°; lit. (2) 5253° ]. An ether solution of the crystals was treated with oxalic acid to form the oxalate. The oxalate was recrystallized from ethanol [m. p. 142-43°; lit. (2) m . p . 144-45.5°].


2

1 2

4

17

e

1 3

5

2

1 2

2 8

2

2


8

78

INTOME

AND

KUHN


Analysis. Calculated for C N 0 : C, 51.04; H, 8.95; N, 5.95. Found: C,50.68; H, 8.42; N, 6.10.) (Elemental analyses were per formed on this compound, because confusion arose from the isolation of the two hydroxylamines.) Ratio of iV-n-Butylhydroxylamine and N, N-Di-n-butylhydr oxylamine Obtained from Reaction Mixture. The hydrochloric acid solution from the hydrolysis of 2 grams of the reaction mixture was extracted with ether to remove small amounts of n-butylboronic acid. The HCl solu tion was made alkaline, treated with sodium diethyldithiocarbamate, and extracted with ether. The ethereal solution was concentrated to yield a mixture of the two hydroxylamines. The hydroxylamines were analyzed by gas chromatography using a Theed column (Fisher Scien tific Co., Fair Lawn, N. J . ) . The mole ratio between N-n-butylhydroxylamine and N, N-di-n-butylhydroxylamine was 2 to 1. (2ST-Nitroso-iV-butoxyamino)dibutylborane, R BN(OR)N=0 (lit). The crude reaction mixture (2 grams) was placed in a three-necked, round -bottomed flask, equipped with a simple distillation head and condenser, and 50 ml. of 10% HCl solution was added. With a slow flow of N through the apparatus, the flask was heated to hydrolyze the top layer. The contents were then distilled into a 50-ml. separatory funnel. At first, di-n-butylborinic acid and water distilled off. Then, the appearance of the distillate changed and the second fraction was collected in another separatory funnel. The combined second frac tions from 12 such experiments were exposed to air for several hours to convert any borinic acid to boronic acid and washed with aqueous mannitol solution. The washed fraction (3. 7 grams) was distilled on a spinning band column (Nester and Faust, 2401 Ogletown Road, New ark, Del.). The fraction (0.3 gram) boiling at 84° at 2. 5 mm. ana lyzed for (iV-nitroso-iN7'-butoxyamine)-di-n-butylborane. Analysis. Calculated for C H B N 0 : C, 59.50; H, 11.16; N, 11 57; B, 4.46; molecular weight, 242. Found: C, 59 49; H, 10.92; N, 11.47; B, 6.01; molecular weight, 277 + 10. The extinction coefficient of the compound was 1020 at 293 πιμ in CC1 and 5000 at 228 πιμ in methanol. Hydrolysis of ΙΠ. One-half gram (2 mmoles) of ΠΙ was refluxed in 10 ml. of concentrated sulfuric acid and 20 ml. of water in a nitrogen atmosphere for 3 hours. The material which collected in a liquid nitrogen trap was found to contain 1. 9 mmoles of nitrous oxide and a mixture of cis- and trans-butene and 1-butene (1. 3 mmoles). Reaction between Tri-n-butylborane and Nitrosobenzene. Nitrosobenzene (1 gram) dissolved in benzene was added dropwise to 1. 7 grams of tri-n-butylborane in benzene. The reaction mixture warms slightly during the addition of the nitrosobenzene. The mixture, amber in color, was allowed to stand overnight. Then the benzene was r e moved under vacuum, yielding a solid residue; the infrared spectra of the residue did not show any NH band of aniline. Methanol was added to the residue but was pumped off when the residue dissolved in meth anol. The residue was hydrolyzed with 50 ml. of water containing 1 ml. of concentrated H S 0 and the volatile matter was distilled off with water. Two fractions were collected. The first fraction (0. 2 gram) was mainly di-n-butylborinic acid. The second fraction (0.1 gram) 1 0


187

5

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2

1 2

2 7

2

2

4

2

4



188

ADVANCES

IN CHEMISTRY SERIES

contained azoxybenzene. The aqueous material in the flask was f i l tered and extracted with ether. The ether solution was concentrated to yield 0.09 gram of w-butylboronic acid. The aqueous portion was neutralized with KOH. The alkaline solu tion was filtered and extracted with ether. The ethereal solution was concentrated to yield 0. 22 gram of residue, which was mainly aniline. After the removal of aniline from the alkaline solution, the solution was acidified. A dark-colored precipitate came out of solution. It was not identified. Reaction of Tri-w-butylborane with w-Butyl Nitrite. To 7. 3 grams (0.04 mole) of tri-w-butylborane, cooled in an ice bath, were added dropwise with stirring 2.0 grams (0.02 mole) of η-butyl nitrite in a slow stream of nitrogen. About 10 minutes after the addition there was a sudden rapid evolution of heat and gas which blew the apparatus apart momentarily at the joint between the reaction flask and the liquid nitrogen trap and also blew some of the liquid reaction mixture into the tubing connecting the two. The reaction mixture was allowed to come to room temperature, and stirred 2 hours. 1-Butene was found in the liquid nitrogen trap. After hydrolysis by refluxing with 10% hydrochloric acid, the upper layer of dibutylborinic acid was removed, and the aqueous acid layer was worked up in the manner described under hydrolysis of tributylborane-nitric oxide reaction product. A n alysis by vapor phase chromatography showed the presence of N-nbutylhydroxylamine and iV,iV-di-w-butylhydrcraylamine. Discussion

of Reaction

Products

Since each of the three major reaction products represents a new type of boron-nitrogen compound, a brief discussion of their proper ties seems in order. Little can be said about R B N R O B R , since we were not able to isolate it from the reaction mixture, nor to synthesize it independently. However, its existence seems to be required to ac count for the products formed upon methanolysis and hydrolysis. The NMR spectrum of ΠΙ has a triplet at 6 = 4.2, referred to (CH ) Si, indicating the presence of a butyl group on oxygen. There are no bands in the region 6 = 2.5, which is characteristic of butyl on nitrogen; hence there are no iNT-butyl groups. Integration of the peaks shows that the ratio of protons on carbon adjacent to oxygen to the remaining protons is 2 to 28. This is compatible with a structure having two butyl groups on boron and one on oxygen, whose ratio would be 2 to 25. The proposed structure for III is 2

3

2

4

R B-N(OR)-N=0 2

Although ΠΙ is not hydrolyzed by boiling in dilute hydrochloric acid, it was successfully hydrolyzed by prolonged refluxing (3 hours) in a solution of 1 part of sulfuric acid to 2 parts of water (vol. /vol. ) to give an approximately quantitative yield of nitrous oxide and a sub stantial amount of butènes acid R B-(OR)-N=0 + H 0 2

^ N 0 + R B O H + ROH

2

ROH

2

a c i d

2

» H Q + butènes 2



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189

The butènes were formed by the isomerization and dehydration of the butanol during the heating in strong acid. The liquid hydrolyzate was inadvertently exposed to air overnight before analysis and therefore showed the presence of n-butylboronic acid rather than the borinic acid required by the above equation. The (N-n-butylamino-oxy)di-n-butylboranes, described in detail elsewhere, are a new and interesting class of compounds. In view of their facile formation from and hydrolysis to di-n-butylborinic acid and JV-butylhydroxylamines, we can be confident of their structures. Synthetic II prepared by the esterification of N, N-di-n-butylhydroxylamine with di-n-butylborinic acid was not absolutely pure, being contaminated with a small amount of di-n-butylborinic acid, as evidenced by a weak OH band at 3627 c m . " Molecular weight in benzene of a 0.05 M solution at 35° shows that it is monomeric (calculated for R N O B R : 269; found: 230 + 20). Crystalline I on the other hand was found to be dimeric, at 35° [calculated for (RNHOBR ) : 426; found: 415 + 20]. The dimer must be either acyclic or cyclic, as illustrated below. The acyclic structure should have two N-H stretching bands in dilute solution, one 1

2

2

2

2

H

R

I

I

R — B ^ o ^ N — R PNHOBR

2

- NHROBR

R — N ^ " ° " " " ^ B — R

2

H Acyclic I

R Cyclic I

due to the tricoordinated Ν at 3400 to 3500 c m . - and one due to the tetracoordinated Ν at about 3200 cm. In the cyclic structure both nitrogens are tetracoordinated. Our compound in fact has only one N-H band in dilute CC1 solution and it is found at 3200 cm. ~ *; hence we believe that it has the cyclic structure. The inability of R N O B R to form a cyclic structure and hence to dimerize can now be explained on the basis of steric hindrance. In the case of (RNHOBR ) there are two axial butyl groups; one is above and the other is below the ring, so there are no axial-axial interactions between two butyl groups. If R N O B R had a cyclic structure, there would be four axial butyl groups: two above and two below the ring. Hence there would be two axial-axial interactions between butyl groups. It is felt that these steric interactions prevent the formation of the cyclic dimer in the case of R N O B R . Reaction Mechanism. A reasonable mechanism by which the ob served products are formed is given in the following series of steps: 1

- 1

4

2

2

2

2

2

2

2

2

RB + NO —• R BNO (1) —R BNOR R BNOR + NO *· RBNO (RN )=0 + NO • RNO + R BNO R BNO + RB • R BNROBR (3) RNO + RB R [NOBR ] —RNOBR (4) RNHOBR+ CH 3

3

(2a)

2

R3BNO

2

(3a)

2

2

3 3

(2)

2 2

R3BNO

2

3

2

2

2


4 8

190

A D V A N C E S IN CHEMISTRY SERIES

The initial adduct formed in step 1 is a free radical which either rearranges (2a) and then reacts with NO to form ΠΙ, or reacts with nitric oxide before rearranging to yield a C-nitroso and a 5-nitroso compound (step 2). Each of these reacts with an R B to yield the hydroxylamine derivatives Π and IV (steps 3 and 4). To account for the 1-butene and RNHOBR which are formed in small but equivalent yield, it is suggested that the intermediate formed in step 4 reacts in two ways: migration of a butyl group from boron to nitrogen to yield the major product (Π), and intramolecular hydrogen transfer from carbon to nitrogen to yield the minor product, 1-butene and I. 3


2

R

o H'"

N

BR

2

Et'

To demonstrate the validity of the proposed mechanism it is neces sary to show that tri-n-butylborane reacts with nitroso compounds to give the type of compound described. We shall report the results of such studies elsewhere. Nitrosobenzene reacts vigorously with t r i - n butylborane and after hydrolysis of the reaction mixture yields d i - n butylborinic acid, in agreement with the proposed mechanism. The amine fraction contained a mixture including aniline andazoxybenzene. Although the reaction with nitrosobenzene differs in detail from the reaction predicted for nitrosobutane, this difference is not surprising in view of the tendency of aromatic nitroso compounds to produce a variety of products in oxidation-reduction reactions. η-Butyl nitrite was also found to react at room temperature with tri-n-butylborane to yield, after hydrolysis, R B O H , ROH, RNHOH, 1-butene, and R N O H . The first step in this reaction appears to be 2

2

RONO + R B 3

^ R B O R + RNO 2

The nitroso compound then reacts with additional tri-n-butylborane to yield I, Π, and 1-butene. Thus the proposed mechanism is consistent with a number of observations. [After this paper was submitted for publication an abstract of a paper on the reaction between triethyl borane and nitric oxide by Brois (1) came to our attention. We are in complete agreement with Brois on the structure of products Π, ΠΙ, and IV, although Brois does not mention I. We are in disagreement with his mechanism.] Acknowledgment We are indebted to Norman S. Bhacca, Varian Associates, for obtaining and interpreting the NMR spectrum of III. We are also i n debted to Roger Bowman of this laboratory for some of the molecular weight determinations and infrared spectra, and to Arthur Garrison of Clemson College, who did some of the early experiments. Elemental In Boron-Nitrogen Chemistry; Niedenzu, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1964.

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191

microanalyses were performed by C. Tiedcke, Laboratory of M i c r o chemistry, Teaneck, N. J .


Literature

Cited

(1) Brois, S. J., Abstracts of Papers, 144th Meeting, ACS, Los Angeles, Calif., April 1963, p. 32M. (2) Dermer, V. H., Dermer, O. C., J. Am. Chem. Soc. 64, 3057 (1942). (3) Douglass, J . E., J. Org. Chem. 26, 1312 (1961). (4) Johnson, D. H., Rogers, M. A. T., Trappe, G., J. Chem. Soc. 1956, 1093. Received May 22, 1963.


Reaction of Nitric Oxide with Tri-n-butylborane - ACS Publications

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