and Dialkylaminotriphenylphosphonium Halides with ...

Reactions of Alkylamino- and Dialkylaminotriphenylphosphonium Halides with Halogens and Interhalogen Compounds; Formation of Alkylaminotriphenylphosphonium Polyhalides Hans Zimmer*, Madhusudan Jayawant, Adel Amer**, and Bruce S. Ault Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, USA Z. Naturforsch. 38b, 103-107 (1983); received September 20, 1982 Halides, I R Spectra, Raman Spectra Alkylamino- and cycloalkylaminotriphenylphosphonium halides react with elemental halogens or interhalogen compounds to afford alkylamino- or cycloalkylaminotriphenylphosphonium trihalides. The stability of these trihalides depends on the cation as well as the trihalide anion. The assignment of a trihalide structure to these compounds was based on elemental analysis and on I R - and Raman spectroscopic evidence. Most stable are the tribromide and [1X2]° salts. During all reactions involving N-alkylamino- and N-cycloalkylaminotriphenylphosphonium halides and elemental halogens an N-halogenation of the cation was not observed.

[Ph 3 P-N-alk] ®Bre

Introduction

In a series of papers we demonstrated the synthetic utility of alkylaminotriphenylphosphonium halides and the corresponding phosphinimines [la-d]. It was shown that alkyl- [la] and cycloalkyltriphenylphosphinimines could be alkylated with iodomethane or -ethane to the corresponding phosphonium salts which upon hydrolysis gave high yields of secondary amines. Recently this reaction was extended to synthesize arylalkylamines by alkylating aryltriphenylphosphinimines [2]. In order to further explore the synthetic utility of alkylaminotriphenylphosphonium salts we planned to N-brominate these salts in order to obtain the corresponding N-bromo-N-alkylamino-triphenylphosphonium bromides. It was thought that aminolysis of these salts in analogy to a modified Raschig synthesis [3] would represent a rather convenient way to alkylhydrazines via hydrolysis of the animated phosphonium salts (eqs (1-3)) [Id]. [Ph3P-N-alk]©Br® + Br2 -

(1)

I H [Ph3P-N-alk]®Br® + HBr

0

ATtJ

K2-IN n

>-

(2)

Br [Ph 3 P-N-alk] ®Br e NR 2 [Ph 3 P-N-alk] ®Bre

strong OH Q

(3)

NR 2 P h 3 P = 0 + R 2 N-NHalk (R = alkyl) However, instead of N-bromination taking place, polyhalide formation was observed (eq. (4)). [Ph 3 P-NHalk] ®X e + Br2 [Ph3P-NHalk]®XBr2®

(4)

While ammonium trihalides have been prepared and studied in some detail, there have been very few reports of the preparation of quarternary phosphonium trihalides [4], Also, in earlier reports on the synthesis of N-alkyl- and N-dialkylaminotriphenylphosphonium halides and the corresponding aryl analogs, no mention of formation of polyhalides has been made [1, 5-10], Results and Discussion

Br * Reprint requests to Dr. H. Zimmer. * * On study leave from University of Alexandria, Egypt. 0340-5087/83/0100-103/$ 01.00/0

To achieve N-bromination the alkylaminotriphenylphosphonium halides were reacted with elemental bromide. It was found that tribromides derived from N-alkylaminotriphenylphosphonium

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104 H. Zimmer et al. • Reactions of Alkylamino- and Dialkylaminotriphenylphosphonium Halides with Halogens

cations form with ease when equivalent quantities of halide salts and elemental bromine are reacted in chloroform solution. f-Butylamino-isopropylamino-, and the unsubstituted aminotriphenylphosphonium cation formed stable tribromides. Cycloalkylaminotriphenylphosphonium tribromides were rather unstable and decomposed to a certain extent during purification attempts. In the presence of water, triphenylphosphine oxide and the corresponding alkylammonium bromide were the only isolated products [Id] (eq. (5)). H20 [(C6H5)3®PNHR]Br3e • (C 6 H 5 ) 3 P=0 + HaNRHBr R=

(5)

A.

The methylamino- and cycloheptylaminotriphenylphosphonium tribromides could not be purified sufficiently for analysis; both yielded after recrystallization only the corresponding alkylaminotriphenylphosphonium bromides, though originally they

Table I. [(C 6 H 5 )3PNHR]©Brö + Br 2

showed a positive KI-starch-iodine test. In Table I the synthesized tribromides are compiled. For identification purposes we relied on the results of the elemental analyses, as well as IR- and Raman spectroscopic evidence. In view of the stability of £-butylaminotriphenylphosphonium tribromide, other trihalides of the /-butylaminotriphenylphosphonium cation were synthesized by applying the method developed for the tribromide formation. Generally it was found that symmetrical trihalides are more stable than unsymmetrical ones. Thus, when f-butylaminotriphenylphosphonium iodide was reacted with ICI the expected I2C19 salt was formed initially; but during purification by successive crystallization from chloroform-ether mixture, the melting point of the salt rose from 144° to 187 °C, the melting point of pure £-butylaminotriphenylphosphonium triiodide. The same behavior was observed on treating the corresponding chloride with elemental iodine; the initially formed Cll2 e salt was identical with the first one and during purification attempts it also gave the triiodide. (eq. (6)).

[(C 6 H 5 )3PNHR]®[Br 3 ]©. Analysis [ % ] N Calcd Found

No.

R,

Formula

Mol.wt.

M.p. [°C] a

Yield

1

H

Ci 8 H 1 7 Br 3 NP

518.05

157-158 b

84.2

2

CH 3

Ci 9 H 1 9 Br 3 NP

532.07

107-108 c ' d

52.1

8

C2H5

C 2 0 H 2 1 Br 3 NP

546.09

121-122 b

71.9

2.56 2.60

4

;-C 3 H 7

C 2 1 H 2 3 Br 3 NP

560.12

161-162 b

89.2

2.50 2.57

5

2-C4H9

C 2 2 H 2 5 Br 3 NP

574.15

146b

93.1

2.44 2.52

6

O

C 2 1 H 2 1 Br 3 NP

558.11

96-97°

65.4

2.51 2.45

C 2 3 H 2 5 Br 3 NP

586.16

130—131C

67.7

2.39 2.40

8

C 2 4 H 2 7 Br 3 NP

600.19

149-150°

63.2

2.33 2.65

9

C 2 5 H 2 9 Br 3 NP

614.21

7

O

99-100 c , d

a Melting points are uncorrected; b crystallized from CHCls/ether; pounds decomposed during purification.

c

52.1

2.70 2.95 -

-

crystallized from ethanol/ether;


d

com-

105 H . Zimmer et al. • Reactions of Alkylamino- and Dialkylaminotriphenylphosphonium Halides with Halogens

[(C6H5)3PNHt • C4H9]©I©+IC1 [(C6H5)3PNHt-C4H9]©Cl©+I2

[(C6H5)3PNHtC4H9]®Cl© + IBr

V

V

[(C6H5)3PNHt-C4H)]®Br© + IC1 [(C6H5)3PNHt • C4H9]®[ClIBr]e

X

recryst. [(C

6

H5)

[(C

6

H

5

PNHt-C

4

H

9

]©[ClI

)3PNHt-C

4

H

9

]+[I

3

3

2

]

—

e

•

-]

If, however, a 1:2 molar ratio of the iodide and IC1 was used, the final product isolated was the [C1IC1]© trihalide. Its formation could be explained by assuming that the originally formed [ C I I 2 ] anion dissociated into Cl e and I 2 ; a subsequent reaction between the Cl e and IC1 led to the isolated 0

[(C 6 H 5 )3PNHt.C 4 H 9 ]®[ClICl] e .

The

formation

of

this salt is in agreement with the fact that mixed polyhalide anions with iodine as the central atom are generally fairly stable. Our observation about the stability of the trihalides derived of the f-butyl aminotriphenylphosphonium cation parallels the order of stabilities of alkali metal trihalides established by Ephraim [11]. Other mixed trihalides were prepared by reacting halides with interhalogen compounds or halogens as illustrated by the following reactions (eqs (7) and (8)).

(8)

X

The polyhalides of the £-butylaminotriphenylphosphonium cations which were prepared during this investigation are listed in Table II. The yield in all cases were good to excellent. That trihalide formation is not restricted to the N-£-butylaminotriphenylphosphonium cation is shown by successful synthesis of a few trihalides derived of other N-alkyl- and N,N-dialkylaminotriphenylphosphonium cations (Table III). All products were stable in the solid state and could be kept for years provided moisture was excluded. Attempts to obtain the desired N-bromo compounds by reacting the triphenyl4-butylaminophosphonium brimide with N-bromosuccinimide yielded a rather unstable colorless compound which gave a positive test with KI-starch reagent. Attempts to purify this compound by crystallization or thin-layer chromatography resulted only in formation of 5. Spectroscopical Investigation

[(C6H5)3PNHt • C4H9]®I© + Br2 [(C6H5)3PNHtC4H9]©Br© + IBr

n

(6)

V x

[(C6H5)3PNHt-C4H9]©[BrIBr]ö

(7)

The infrared spectra, in the region 200-4000 cm -1 , were similar for all compounds and showed usually a rather broad peak in the 3240-3350 cm -1 region

Tab. II. [(C 6 H 5 ) 3 PNH-f-C 4 H 9 ]©X© + Y 2 -> [(C 6 H 5 ) 3 PNH-*-C 4 H 9 ]®[XY 2 ]©a. Analyses [ % ] C H N Cl Calcd Calcd Calcd Calcd Found Found Found Found

No.

XY2-

Formula

Mol.wt.

M.p. [o C j a ,b

Yield

1

BrCl 2

C 22 H 25 BrCl 2 NP

485.23

144-145

85.2

-

-

2.89 2.85

14.61 14.37

2

IC12

C 22 H 25 C1 2 INP

532.22

157

84.1

-

-

2.63 2.69

13.32 12.96

3

Br 3

C 2 2 H 2 5 Br 3 NP

574.15

146

93.1

4.39 4.42

2.44 2.52

4

IBr 2

C 2 2 H 2 5 Br 2 INP

621.14

160

90.2

-

2.25 2.28

5

I3

C 2 2 H 2 5 I 3 NP

715.14

188-189

95.5

3.52 3.56

1.96 2.27

6

ClIBr

C 22 H 25 BrClINP

576.68

160

86.7

-

-

2.43 2.34

7

Brl2

C 2 2 H 2 5 BrI 2 NP

668.14

170

81.4

—

—

2.09 2.06

a

Compounds crystallized from CHCl 3 /ether;

b

46.03 45.99 -

36.95 37.01

melting points are uncorrected.


Br Calcd Found 16.47 16.19

_

-

41.77 41.78

-

25.73 25.38

-

6.15 6.08 —

-

13.86 13.92 —

I Calcd Found -

23.84 23.85 -

20.43 20.34 -

22.01 22.03 —

106 H. Zimmer et al. • Reactions of Alkylamino- and Dialkylaminotriphenylphosphonium Halides with Halogens

Table I I I .

•Ri

(C 6 H 5 ) 3 P-N: \R2

X© + Y 2

(C 6 H 5 ) 3 -PN:

/RI \R2

[XY2]©Z.

Analyses [ % ] N Calcd Found

No.

RI

R2

XY2-

Formula

Mol.wt.

M.p

1

(CH 3 ) 2 CH

H

Brl 2

C 2 iH 2 3 BrI 2 NP

654.11

142- 143B

92.3

2.14 2.12

2

CH 3

(CH 3 ) 3 C

IBr 2

C 2 3 H 2 7 Br 2 INP

635.17

167

90.5

2.20 2.13

3

CH 3

(CH 3 ) 3 C

IS

C 2 3 H 2 7 I 3 NP

729.17

209- 210

93.0

1.92 1.93

a

Melting points are uncorrected;

13

[°C]a,b

Yield

crystallized from CHCl 3 /ether.

characteristic of the NH-stretching mode of the cation. For the Raman spectroscopic investigation compounds 1,3 (Table II) and [Ph3PNH-t-C4H9]©Br© [la] were selected. The Raman spectra of compounds 1 and 3 (Fig. 1), in the low frequency region

100 300 R A M A N SHIFT, cm-1

100-500 cm--1 showed spectra characteristic of each anion. The Raman spectrum of the Br 3 e salt was dominated by an intense line at 167 cm -1 , within 1 cm -1 of the literature value for the symmetric stretching mode of the Br 3 e anion [12]. In addition, a weak line was observed at about 330 cm -1 , cor-

responding to the first overtone of the symmetric stretching mode, indicating some resonance enhancement of the signal. The Raman spectrum of the BrCl2e salt showed two weaks lines, at 163 and 275 cm -1 while the Br© salt showed no Raman lines in the low energy region. The Raman spectra strongly thus support the existence of the trihalide anions in these salts. The Raman spectra also provide some information as to the local environment of the anion. For Br3©, an intense Raman line was observed for vi. the symmetric stretching mode, while no hint of a line was observed near 190 cm -1 , where v3, the antisymmetric stretching mode should be observed. This mode is Raman inactive [13] if the anion maintains a center of symmetry, but should be activated if the anion is distinctly perturbed in the crystal. The Raman spectrum of the BrCl2© salt was less intense, and somewhat less definitive, showing lines at 163 and 275 cm -1 . The upper line is in good agreement with the symmetric stretching mode of the centrosymmetric BrCl2© anion, but again only one vibrational mode is anticipated for this species. The Raman line at 163 cm -1 may indicate that the anion is not centrosymmetric, but distorted or even chlorine-centered, BrClCl©; this species should have Raman stretching modes in both of these spectral regions. Alternatively, the 163 cm -1 line might be attributed to a small amount of Br3© impurity. Further support for lack of N-bromination but formation of trihalide anions instead during these reactions comes from 31P-investigations of [Ph3P-NHC(CH3)3]®Br© and compoundsl (Table II). The observed values were d —31.156 and —31.196 with H3PO4 as external standard. These values are


107 H . Zimmer et al. • Reactions of Alkylamino- and Dialkylaminotriphenylphosphonium Halides with Halogens

To a magnetically stirred, ice-cold solution of cycloalkyl or alkylaminotriphenylphosphonium bromide in chloroform an equimolar 10% solution of bromine in chloroform was added dropwise. Temperature was not allowed to exceed 10 °C during addition and an inert atmosphere was maintained over the reaction mixture. When the reaction was over, chloroform was evaporated at temperatures below 50 °C and the residue was triturated with dry ether. In the cases of low melting solids, an orange viscous oil was obtained after removal of the solvent and this was triturated with ether. Aminotriphenylphosphonium tribromide and ethyl-, isopropyl- or £-butylaminotriphenylphos-

phonium tribromides were precipitated directly from chloroform solutions by addition of dry ether. They were purified by crystallization from chloroform-ether. In case of methyl-, cyclopropyl-, cyclopentyl-, cyclohexyl-, and cycloheptyl-aminotriphenylphosphonium tribromides, however, chloroform was removed as completely as possible before crystallization either from ethanol or from ethanol-ether mixtures was attempted. Crystallizations of these compounds proceeded very slowly and decomposition to the corresponding phosphonium bromides or the primary amine hydrobromides plus triphenylphosphine oxide was extensive. t - Butylaminotriphenylphosphonium polyhalides; general procedure: These polyhalides were synthesized according to the above procedure. The following halogens or interhalogen compounds were used for the reaction with t- butylaminotriphenylphosphonium chloride, bromide or iodide: CI2, Br2, I2, IC1, and IBr. Reactions with chlorine were carried out by bubbling a slow stream of dry chlorine gas into an ice-cold 10% solution of the appropriate phosphonium halide in chloroform. The amount of chlorine absorbed was measured by gain in weight. The trichloride decomposed readily. Secondary reactions observed in the case of £-butylaminotriphenylphosphonium iodide - iodine monochloride, and t-butylaminotriphenylphosphonium iodide chlorine reactions were the result of increased proportions of halogen or interhalogen compounds. They are described in the discussion section. N,N-Dialkylamino- and i-propylaminotriphenylphosphonium polyhalides Table III: Conditions as above were used to react N-methyl,N-£-butylaminotriphenylphosphonium iodide with bromine or iodine and of isopropylaminotriphenylphosphonium bromide with iodine. To the reaction mixture in chloroform, 50 ml dry ether was added to precipitate the corresponding polyhalides, which were filtered off, dried and purified by recrystallization.

[1] a) H . Zimmer and G. J. Singh, Org. Chem. 28, 483 (1963); b) H . Zimmer and G. Singh, Angew. Chem., Int. Ed. Engl. 2, 395 (1963); c) H . Zimmer and G. Singh, J. Org. Chem. 29, 3412 (1964); d) H . Zimmer, M. Jayawant, and P. Gutsch, J. Org. Chem. 35, 2826 (1970). [2] E. M. Briggs, G. W . Brown, J. Jiricny, and M. F. Meidine, Synthesis 1980, 295. [3] L. F. Audrieth, U. Scheibler, and H . Zimmer, J. Am. Chem. Soc. 78, 1852 (1956). [4] a) G. Wittig and G. Geissler, Justus Liebigs Ann. Chem. 580, 44 (1953); b) D. Kanai, T. Hashimoto, H. Kitano, and K . Fukui, Nippon Kaguku Zasshi 86, 534 (1965); C. A . 63, 6586 c (1965); c) G. P. Schiemenz, Chem. Ber. 98, 65 (1965). [5] I. N. Zhmurova, A. A. Kisilenko, and A. V . Kirsanov, Zh. Obschch. Khim. 32, 2580 (1962);

J. Gen. Chem. U S S R 32, 2544 (1962). [6] D. F. Clemens, W . Woodford, E. Dellinger, and Z. Tyndall, Inorg. Chem. 8, 998 (1969). [7] R . Appel, K . Kleinstück, D. Ziehn, and F. Knoll, Chem. Ber. 103, 3631 (1970). [8] R . Appel, Angew. Chem. 85, 863 (1975); Angew. Chem. Int. Ed. Engl. 14, 801 (1970). [9] K . Fukui and R . Sudo, Bull. Chem. Soc. Jpn. 43, 1160 (1970). [10] H.-J. Cristeau, A . Chene, and H . Christol, Synthesis 1980, 551. [11] F. Ephraim, Ber. 50, 1069 (1917). [12] W . Gabes and H . Gerding, J. Mol. Struct. 14, 267 (1972). [13] K . Nakamoto, "Infrared and Raman Spectra of Inorganic and Coordination Compounds" 3rd ed. Wiley-Interscience, New York 1978. [14] P. Beck, in G. M. Kosolapoff and L. Maier (eds.): Organic Phosphorus Compounds, Vol. 2, Chapter 4, Table 16, Wiley-Interscience, New York 1972.

well in the range of 31P chemical shifts of aminotriphenylphosphonium salts [14], thus showing that no structural changes in close proximity of the P-atom occurred. Experimental

Infrared spectra were recorded in Nujol mulls on a Beckman IR-12 infrared spectrophotometer, while Raman spectra were taken of the powdered material in capillary tubes. These spectra were recorded on a Spex Ramalog spectrometer, after excitation by either the 4880 A or the 5145 Ä line of an argon laser (Coherent Radiation). Slight decomposition of the Br3e and BrCl2e salts was observed when 5145 Ä excitation was employed, and considerable decomposition was noticed when the 4880 Ä line was used. The BrCl2e was particularly susceptible to decomposition, and consequently less intense Raman lines were obtained. The 31P NMR spectra were obtained with a Bruker HX-90 model in DMSO-d6 solution. Melting points were uncorrected. The microanalyses were done by Galbraith Laboratories, Knoxville, TN. Alkyl- and cycloalkylaminotriphenylphosphonium tribromides- general procedure
