Amination of Borate Esters with Diamines - Advances in Chemistry

19 Amination of Borate Esters with Diamines EUGENE J . MEZEY, PETER R. GIRARDOT, a n d WILLIAM E. BISSINGER

Downloaded by CALIFORNIA INST OF TECHNOLOGY on January 9, 2017 | http://pubs.acs.org Publication Date: January 1, 1964 | doi: 10.1021/ba-1964-0042.ch019

Chemical Division, Barberton, Ohio

Barberton

Laboratories,

Pittsburgh

Plate Glass

Co.,

Alkoxyboranes can be aminated with amines and diamines at moderate temperatures. To facili tate this aminolysis with aromatic diamines of high molecular weight, a solvent was found nec essary for certain alkoxyboranes that otherwise formed two-phase systems with the diamines and did not react. Linear polymers were produced from dialkoxyborane and diamines, while highly cross-linked polymers were produced when trialkoxyboranes and diamines reacted. A minoboranes and other boron-nitrogen bonded compounds are readily solvolyzed in alcohols of low molecular weight, at least up to C . In such reactions, the boron-nitrogen bond is replaced by a boron-ox ygen bond and the corresponding amine is liberated in the forward reaction: 4

/BNHR + R'OH Ζ ^ B O R + R N H T

(1)

2

Under special conditions, the converse reaction, amination of borate esters, proceeds easily. While earlier reports (4, 5, 7,9) suggested that the amination is difficult, Letsinger and Hamilton (10) and Brotherton and Steinberg (3) have shown that the reaction is driven toward amination when the boron-containing species can enter intofive-membered ring formation with o-phenylenediamine, but is more difficult with aniline and p-phenylenediamine. Another factor, removal of the alcohol from the reaction mixture, was recognized by Mikhailov and Aronovich (12), who reported the rates of alcohol removal and, by inference, their dependence upon the base strengths of the amines. In some cases the aminations were 90% complete. A tentative series of reactivities for the ability toward displacement of various groups has been proposed (1,13,14), subject to polar, steric, and volatility factors : -OR > - N H > - N H 2

2

3

> -NHNR

2

> -NHR > - N R

2

in the conversion of JB-triaminoborazines to J5-trialkoxyborazines by treatment with alcohols and in their transaminations with amines. The reversal of at least part of this order was further confirmed during the present investigation, and the influence of the volatility fac192

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

19

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193

tor was observed. Although Brotherton and Steinberg did not report the nature of the product from the reaction of triisopropoxyborane and />-phenylenediamine, it could be inferred that a polymer formed. In this investigation we have examined the reaction of diamines with both trialkoxyboranes and dialkoxyboranes and made a brief investigation of the polymers formed. During the work it was found that the solvent, xylene, was effective in reversing the direction of Reaction 1, since it eliminated immiscibility of the reactants. Other similar solvents could undoubtedly be used. Downloaded by CALIFORNIA INST OF TECHNOLOGY on January 9, 2017 | http://pubs.acs.org Publication Date: January 1, 1964 | doi: 10.1021/ba-1964-0042.ch019

Experimental Materials. Trimethoxyborane (Callery Chemical Corp. ) was dis tilled (b.p. 67°C.)before use. Triisobutoxyborane was prepared from B C 1 and isobutyl alcohol. Distillation yielded a fraction boiling at 207° C . with an index of refraction, n^ , 1.4037 (lit. 1.4029). Phenyldiisobutoxyborane was prepared from phenylboronic acid, PhB (OH) (American Potash and Chemical Corp.), and isobutyl alcohol by the azeotropic removal of water. Anal. Calcd. : B, 4.62. Found: B, 4.53, 4 . 5 2 w ^ 1.4705 [lit. (2) 1.4711]. The amines were commercially available and were recrystallized and dried whenever a technical grade material was used. Apparatus. The driving force for the amination reactions was the rapid removal of the alcohol. This was conveniently done by continuous distillation with a fractional distillation column of about 30 theoretical plates equipped for total reflux and controlled take-off. An alkoxyborane was first fractionated in such a column, then the same column was used to separate the reaction products from an amine and the same alkoxy borane. The still pot served as a reaction vessel. The boranes were handled with hypodermic syringes to assure minimum contact with moisture. High vacuum techniques were used for some of the separa tions and sampling operations. A l l the equipment was purged with either dry air or nitrogen. Procedure 1. Trimethoxyborane and p,p'- Methylenedianiline. T r i methoxyborane (53.9 mmoles) was added to 21.8 mmoles of p,p methylenedianiline (Dow Chemical Co.). The temperature was raised to 67° and (CH 0) Β was observed to reflux. The reflux temperature gradually dropped to that of the boiling point of the methanol-trimethoxyborane azeotrope [b.p. 53.2°; 76.2% (MeO) B; lit. b.p. 54.6°;68% (MeO) B ] . The azeotrope was removed over a period of 22 hours. Occasionally, a period at total reflux was necessary to build up the aze otrope concentration in the head of the column after the removal of some of the azeotrope. After no additional azeotrope was observed, 17.9 mmoles of trimethoxyborane was removed through the distillation column. The pot residue was a hard opaque material which did not soften at 230°, but only when it was heated in a Meker burner flame. On exposure to air, Ρ,Ρ'-methy lenedianiline formed on its surface and was identified by a mixed melting point with the starting material (m.p. 89-93° ; lit. m. p. 89.5°)· Anal. Calcd. for Ito 1 polymeric product: B, 4.54;diamine, 82.9. Found: B, 2.47; diamine, 83.2. The diamine was weighed as free amine after alkaline hydrolysis of a sample of the polymer and isolation and drying of the diamine. 3

20

2

;

r

3

3

3

3


A D V A N C E S IN CHEMISTRY SERIES

194

Procedure 2. Trimethoxyborane and Aniline. A mixture of 98.8 mmoles of aniline and 98.8 mmoles of trimethoxyborane was refluxed for 21 hours at 68° ; the reactants were completely miscible. No change in the reflux temperature was observed. Procedure 3. Triisobutoxyborane, (C HQ 0) B, and p, />'-Methylenedianiline. When 48.2 mmoles of p, />'-methylenedianiline was added to 46.0 mmoles of (Q HgOjg Band heated for 8 hours at the reflux temperture of the borane, 207°, no drop in the reflux temperature was observed. Two phases were noted in the still pot, the lower layer being the dia mine. Vigorous stirring did not promote reaction. Procedure 4. Triisobutoxyborane and p, £'-Methylenedianiline in Xylene. Commercial (mixed) xylene (20 m l . , b. p. 137-40° j r c ^ 1.495-1.505) which had been dried over sodium was added to the reac tants in Procedure 3. At 140°, the reflux temperature, the borane and diamine were miscible with stirring. The reflux temperature slow ly dropped from 136° to 105-06° (b.p. isobutyl alcohol, 106-08°) in 1 hour. Over a period of 32 hours, 63.4 mmoles of isobutyl alcohol was removed (np20 1.4102; lit. 1.3958). At the end of the time period, butanol evolution ceased. Some of the isobutyl alcohol was recovered from the redistillation of the xylene. Unreacted triisobutoxyborane [Anal. Calcd. Β, 4.70. Found: B, 4 . 1 2 ; n 1.4065 (lit. 1.4029)] was recovered from the reaction pot by distillation. The difference in weight between the starting diamine and the polymeric residue was equiv alent to a weight gain of 55. 8 grams per mole of borate ester con sumed. It would be expected for a 1 to 1 linear polymer that a C HgOBC group would be attached to each diamine and that the weight gain would be theoretically 83. 9 grams per mole of borate ester consumed. The weight gain for total amination and thereby cross linkingwould be 10.8 grams per mole of borate ester consumed. The polymeric residue was opaque, hard, and brittle. An odor of isobutyl alcohol persisted over the solid. It did not soften at 230° but on heating in a Meker burner flame it became fluid. The product lacked hydrolytic stability, releasing the diamine at the exposed surface. Procedure 5. Triisobutoxyborane and p-Toluidine in Xylene. To 20 ml. of xylene were added 48.7 mmoles of />-toluidineand40.6mmoles of triisobutoxyborane. After 21.2 mmoles of isobutyl alcohol was collected over a 24-hour period, the reaction slowed down to the point that an additional 16 hours of heating gave but a few drops more of the alcohol. An additional 101.1 mmoles of £-toluidine was added and the mixture heated for 83 hours at 140°. A total of 88.2 mmoles of isobutyl alcohol was collected with some loss during collection over the total of 123 hours. Three cuts of the xylene-isobutyl alcohol mixture were taken over the total time period. Each cut was weighed and the percent xylene in each cut was determined by gas-liquid chromatography. T r i s P-toluidinoborane crystallized from the xylene in the still pot in a crude yield of 88.7%. Recrystallization from benzene gave well defined crys tals [m.p. 165° ; lit(8) , 165-66° ]. Anal. : Calcd. (CH C H4 NH) B, 3.29. Found: B, 3.84, 3.35. Unreacted />-toluidine (25.3mmoles) was recovered [m.p. 45 (lit. 45°)]. The data from Procedures 1 to 5 are summarized in Table I. Procedure 6. Phenyldiisobutoxyborane and Diamines in Xylene (Table II). p, p'-Methylenedianiline. The 48.9 mmoles of the diamine


4

3

D

2 0

4

3

e


3

19

ME1EY ET AL

Amination

of Borate Esters

195

and 57.3 mmoles of PhB(C HgO) were mixed with 17.4 grams of xylene and heated to 140°. The isobutyl alcohol-xylene mixture was collected in three fractions during the 27-hour reaction time. The per cent xylene was determined in each. A total of 97.5 mmoles of isobutyl alcohol was collected. Theoretical for the 48.9 mmoles of diamine used was 97.8 mmoles. Unreacted borane, P h B ( O C H ) , was recovered (6.8 mmoles) from the reaction product. Filaments could be drawn from the residue at 70°. The polymeric residue became fluid at about 110° and onfurther heating up to 320° under reduced pressure it lost a clear liquid containing boron value and during heating became more viscous. The cooled residue after vacuum treatment nowbecame fluid at 190° at atmospheric pressure under nitrogen. Filaments could be pulled from the soft mass. At room temperature thev were flexible, but hydrolyzed in air after 1 hour. N, AT-Diphenyl-/>-phenylenediamine. To 20 m l . of xylene were added 50.7 mmoles of the diamine (Naugatuck Chemical Division, U. S. Rubber Co. ) and 51. 0 mmoles of PhB(OC Hg ) . A single xylene -isobutyl alcohol cut, collected over the 165-hour reaction time, contained 87.1 mmoles of isobutyl alcohol. After reduced pressure heating , the product resembled pitch and filaments could be pulled from the softened material. The product lacked hydrolytic stability. Unreacted pheny ldiisobutoxyborane was recovered from the reaction (0.9 mmole). When 16.5 mmoles of the diamine and 28.1 mmoles of PhB(OC H ) were sealed in aborosilicate glass tube and heated to 300° for 30 hours, no change was observed in the physical appearance of the diamine. Piperazine. Recrystallized piperazine (Union Carbide Chemical Corp., 55. 8 mmoles) reacted with 53. 0 mmoles of PhB(OC Hg ) in 20 ml. of xylene at 140°. Isobutyl alcohol was observed during the 30hour run by a drop in reflux temperature to 108° . Some piperazine was carried over (b.p. 145°) by the xylene. The product had a crystalline appearance and had no polymeric properties. N, W-Diphenylethylenediamine. The 50 mmoles of P h B ( O C H g ) in 25 ml. of xylene was added dropwise to 51.8 mmoles of the diamine (Distillation Products Industries) in 28 ml. of xylene which was heated to 140°. The reflux temperature did not drop during the addition and only after all of the borane had been added did the temperature drop to 108° C , indicating isobutyl alcohol was being evolved. The amount released could not be determined because of solvent loss. The solid, after vacuum treatment and heating, cooled to a definite crystalline habit and had no polymeric properties. />-Toluidine. To 20 ml. of xylene were added 25. 8 mmoles of PhB (OC H ) and 56.0 mmoles of toluidine (Distillation Products Industries). The reaction was heated to 140° and an isobutyl alcohokxylene mixture was found to contain 47.6 mmoles of isobutyl alcohol, or 92% of the theoretical. 4

2


4

4

9

2

2

4

4

9

2

2

4

4

9

2

2

Discussion This work has in general confirmed the findings of Mikhailov and Aronovich (12) and Brotherton and Steinberg (3) . They, with others Niedenzu; Boron-Nitrogen Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1964.


196

Table I.

Reaction Temp., ° C

Amine, Mmoles

(RO)3B, Mmoles

p, />-Methylenedianiline

21.8

R=CH 53.9

Aniline

98.8

p, p '-Methylenedianiline

48.2

R=C H 46.0

207


48.2

R C H0'

140

Amine


Reactions

67.2

3

R=CH 98.8 3

4

=

67.2

9

4

46.0 p

149. 8

-Toluidine

140

R=C H -

b

4

9

40.6 Part of (MeOJgB recovered as azeotrope with MeOH produced. With 48.7 mmoles toluidine, reaction ceased after 40 hours and 101.1 mmoles added. Part of butanol lost during collection.

Table II.

Amine

Amine, Mmoles

PhB(OC H ) , MMoles 4

9 2

Reactions of (Xylene Reaction Temp. °C>


48.9

57.3

140

N, iV'-Diphenyl-/> -phenylenediamine

50.7

51.0

140

Piperazine

55.8

53.0

140

N, N'-Diphenylethylenediamine

51.8

50.0

140

(6 10,11,15), have successfully aminated borate esters, reversing the reported trend of displacement (1,13,14). They did not, however, r e port on polymeric products that may have been formed from the reactions of diamines with trialkoxyboranes and with phenyldialkoxyboranes. The reactions reported here are extended to other diamines and to the polymeric products formed from difunctional and trifunctional boranes. Mikhailov and Aronovich aminated the isobutoxy esters of boric acid and its aryl derivatives with aromatic monoamines of moderate molecular weight in the presence of excess amine and at the boiling point of the amine. The reaction temperatures they reported ranged f


19

ME1EY ET AL

Amination

197

of Borate Esters

of (RO) B with Amines 3

Time, Hours


Solvent

ROH, Mmoles

Recovered (RO) B, Mmoles 3

Remarks Polymer, highly crosslinked, >230° softening point

None

22

23.8

None

21

None

No azeotrope formed

None

8

None

No butyl alcohol, 2 phases present

Xylene

32

63.4

Xylene

123

41.7

e

Polymer, highly c r o s s linked, >230° softening point

17.1

36. 0 mmoles B ( N H C H C H ) and 25. 3 mmoles toluidine recovered

88. 2

C

6

PhB(0-i-C H ) solution) 4

9

2

9

3

g

with Diamines Recovered

Time,

Hours 27

ISO-C HQOH, 4

Mmoles 97.5

PB(OC Hg) , 4

2

Mmoles 6.8

Remarks Polymer, m.p. -190°

165

87.1

0.9

Pitchlike polymer

30

Obsd.

—

Piperazine carried over; residue crystalline

22

Obsd.

—

Liquid residue, crystallized at 25°

from 210° to 250°. At these temperatures, it must be assumed that the borate esters and the amines were miscible. In a specific case, triisobutoxyborane reacted with/>-toluidine (b.p. 200°) to yield isobutyl alcohol within an 8-hour reaction time, and in our laboratories, these were found to be miscible. Inour work, however, p, p -methy lenedianiline and triisobutoxyborane were immiscible at or above 207° (the boiling point of the ester) and after 8 hours no butanol was isolated even with stirring. The base strength and steric requirements of />-toluidine would not be expected to be much different than those of / ^ ' - m e t h y l e n e dianiline. The only difference in their reactivity appears to be the lack r


198


of miscibility of the high molecular weight diamine with the borate ester. At 25° and 300° C . , N,N'-diphenyl-p-phenylenediamine wasfoundtobe immiscible with phenyldiisobutoxyborane in a sealed borosilicate glass tube. In each of the above cases, when the solvent, xylene, was added to the reaction mixture, the reactants were miscible, and isobutyl alcohol was released at 140°. The amination reaction took place slowly and the steric and base strength effects of the diamines were evident from the rate of isobutyl alcohol removal (Tables landII), and in accord with the literature (12) . When p, p -methylenedianiline reacted with trimethoxyborane, no solvent was needed, since the two were miscible and they reacted at the reflux temperature of the borane (67° ). Xylene as a reaction medium was used by Brotherton and Steinberg (3) in their amination of triisopropoxyborane with aniline. The effect of the type of solvent used was illustrated when only a slow reaction occurredbetween p- pheny lenediamine and triisopropoxyborane in xylene, but when bis (2-ethoxy ethyl) ether (b.p. 187-89°) was used as a solvent, the same reactants yielded isopropyl alcohol more readily, perhaps because of the higher temperature of the reaction. They did not mention whether the reaction failed without a solvent. Although not described, the product of the diamine-triisopropoxyborane reaction may have been a cross-linked polymer, on the basis of our results (Table I). The polymeric materials from p,p methylenedianiline and triisobutoxyborane or trimethoxyborane were probably cross-linked because of the trifunctionality of the borate esters. Evidence for the formation of a three-dimensional network was in part based on the physical properties of the products. They were hard, hornlike substances that softened only at temperatures greater than 230°. Filaments could not be pulled from the softened material, indicating a lack of linearity in the product. Further evidence was obtained from the stoichiometry of the borate ester consumed in the diamine reaction. The 28.9 mmoles of triisobutoxyborane that reacted was equivalent to 86.7 mmoles of butoxy groups attached to the boron and the 48. 2mmoles of diamine, in turn, was equivalent to 96.4 mmoles of amine groups. . The 63. 4 mmoles of isobutyl alcohol recovered from the reaction was 73% of the amount expected for complete amination. Although the reactants were present in a 1 to 1 mole ratio at the beginning of the reaction, the diamine reacted to eliminate a majority of all of the butoxy groups on a given boron and triisobutoxyborane was recovered from the reaction. That all of the butoxy groups could be eliminated was in part confirmed when the totally aminated borane, tri-p-toluidinoborane, was prepared from p-toluidine and triisobutoxyborane in xylene at 140°. An excess of amine was necessary for the 88.7% yield obtained. In the case of trimethoxyborane, the borate ester was in excess at the beginning of the reaction (53. 9 to 21. 8 mmoles). Trimethoxyborane was recovered from the reaction partly as the azeotrope with methanol during the reaction and, after the reaction appeared to cease, as the pure material. The 12.2 mmoles of trimethoxyborane consumed was equivalent to 36. 6 mmoles of methoxy groups, while the diamine was equivalent to 43. 6 mmoles of amine groups. The diamine, being func-


r

L


79

MEZEY ET AL

Amination

of Borate Esters

199


tionally in excess, may thus have totally aminated all of the borate ester that was consumed and thereby led to the formation of the crosslinked polymer. The methanol recovered was 65% of the theoretical expected from total amination. When the difunctional phenyldiisobutoxyborane reacted with/>, />'methylenedianiline, the reaction proceeded faster than with triisobutoxyborane and the amination was complete on the basis of the isobutyl alcohol recovered. This faster rate of amination is in agreement with the findings of Mikhailov (12). The polymer that formed was not cross-linked and the filaments could be drawn from the heat-softened material. From this, it appears that at this temperature only one hydrogen of each amine group has reacted with borate ester. With N, iV'-diphenyl-p-phenylenediamine, the isobutyl alcohol evolution was much slower, possibly because of the base strength and steric effects of the secondary amine. This trend was also observed by Mikhailov (12)· The polymeric product was likewise linear, since filaments could be drawn from the heat-softened material. The solid products from the reaction of phenyldiisobutoxyborane with piperazine or N, N -diphenylethylenediamine did not have polymeric properties. Five-membered borole ring formation cannot be ruled out in either case and may account for the crystalline appearance of the products. As pointed out by Mikhailov and Aronovich, heating an aminoborane , such as phenyldi-/>-tolylaminoborane, to 260° to 270° will cause borazine formation by deaminat ion. At the temperatures at which the aminated products were formed in their work, this side reaction cannot be ruled out, although it was minimized in our work by the lower amination temperatures possible in a solvent, as illustrated by the high yield of tritoluidinoborane obtained in this work. Although trimethoxyborane reacted with p, methylenedianiline in 22 hours without a solvent, aniline did not react under the same conditions in 21 hours. Jones and Kinney (7) also found that triethoxyborane did not react with aniline. However, Brotherton and Steinberg (3) reported that in the presence of xylene, triisoproxyborane reacted slowly with aniline to form trianilinoborane, while Mikhailov and Aronovich (12) found that a solvent was not necessary to aminate triisobutoxyborane with aniline at 184° to form triianilinoborane. The differences in the reactivities of the different types of borate esters with aniline are outside the scope of this investigation and a subject of another investigation. A l l of the polymeric materials produced in this work could be heated in nitrogen to 320° without charring; however, they all lacked hydrolytic stability in air. In the amination of trimethoxyborane, triisobutoxyborane, and phenyldiisobutoxyborane, we have relied on the higher volatility of methanol and isobutyl alcohol. Their removal from the reaction mixture which contained the less volatile borate esters, amine or diamine, and the boron-nitrogen compound made it possible for the aminolysis reaction to proceed. If the amine was volatile, the reaction was only partially effective, as shown by piperazine (b.p. 145). The amination did not occur unless there was an intimate contact between the borane and the amine, which was accomplished by xylene. Other solvents may be even r


200


more effective. For the total amination of a borate ester, an excess of the amine appears to be necessary. Acknowledgment The authors are indebted to Z. Nagy and R. Pfost for assistance in the gas chromatographic analyses.


Literature

Cited

(1) Aubrey, D. W., Lappert, M. F . , Proc. Chem. Soc. 1960, 148. (2) Brindely, P. Β., Gerrard, W., Lappert, M. F., J. Chem. Soc. 1955, 2956. (3) Brotherton, R. J., Steinberg, H . , J. Org. Chem. 26, 4632. (1961). (4) Gerrard, W., Lappert, M. F . , Pearce, C. Α . , Chem. Ind. (London) 1958, 292. (5) Gerrard, W., Lappert, M . F . , Pearce, C. Α . , J. Chem. Soc. 1957, 381. (6) Goubeau, J., Ekhoff, Ε., Z. Anorg. Chem. 268, 145 (1952). (7) Jones, R. G . , Kinney, C. R., J. Am. Chem. Soc. 61, 1378 (1938). (8) Kinney, C. R., Kolbezen, M. F . , Ibid., 64, 1548 (1942). (9) Kuivila, H. G . , doctoral thesis, Harvard University, Cambridge, Mass., 1948. (10) Letsinger, R. L., Hamilton, S. B . , J. Am. Chem. Soc. 80, 5411 (1958); J. Org. Chem. 25, 592 (1960). (11) May, F. H . , Levasheff, V. V. (to American Potash and Chem ical Corp.), U. S. Patent 2,824,787 (1958). (12) Mikhailov, Β. Μ., Aronovich, P. Μ., Zhur. Obschchei Khim. 29, 3129 (1959). (13) Niedenzu, Κ., George, W., Dawson, J . W., Abstracts of Papers, 140th Meeting ACS, Chicago, Ill., 1961, p. 15N. (14) Niedenzu, K . , Harrelson, D. H . , Dawson, J . W., Chem. Ber. 94, 671 (1961). (15) Quill, L. L. Ogle, P. R., Kollander, L. G., Lippincott, W. T . , Abstracts of Papers, 129th Meeting, ACS, Dallas, Tex., 1956,p. 40N. Received May 16, 1963.


Amination of Borate Esters with Diamines - Advances in Chemistry

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