Cleavage and Formation of P-C Bonds during an Unusual Kinnear-Perren Reaction

Article abstract of DOI:10.1515/znb-1998-1104

Treatment of triphenylmethyldichlorophosphine 1 with aluminium trichloride in the presence of tert-butyl chloride leads, after hydrolysis, with high selectivity to di-tert-butylphosphinic chloride 5. The reaction is suggested to proceed via a chlorophosphinidene intermediate which is trapped by the alkyl chloride.

Full text of DOI:10.1515/znb-1998-1104

I
Cleavage and Formation of P-C Bonds During an Unusual
Kinnear-Perren Reaction
Volker Plack, Jens R. Goerlich, Reinhard Schmutzler*
Institut für Anorganische und Analytische Chemie der Technischen Universität,
Postfach 3329, D-38023 Braunschweig, Germany
Z. Naturforsch. 53 b, 1265-1266 (1998); received June 25, 1998
Kinnear-Perren Reaction, Triphenylmethyl
Treatment of triphenylmethyldichlorophosphine 1 with aluminium trichloride in the presence
of tert-buty\ chloride leads, after hydrolysis, with high selectivity to di-terf-butylphosphinic
chloride 5. The reaction is suggested to proceed via a chlorophosphinidene intermediate which
is trapped by the alkyl chloride.
tions using tert-butyl chloride as an alkyl halide,
Introduction
and triphenylmethyldichlorophosphine 1 [16] as a
nucleophile. Surprisingly, after hydrolysis, di-tert-
butylphosphinic chloride 5 [17, 18] was obtained
as the only phosphorus-containing compound. Ap-
parently, cleavage of the P-C-bond between the tri-
phenylmethyl group and phosphorus was accompa-
nied by the formation of P-C bonds between two
tert-butyl groups and the latter.
Formation of a phosphorus-carbon bond is ob-
served when phosphorus trichloride as a nucleophile
attacks the electrophilic carbon atom of an activated
alkyl halide. If the Lewis acid aluminium trichloride
is used, in order to activate the alkyl halide, and the
ionic intermediate complex is finally hydrolyzed to
give alkylphosphonic dichlorides, this sequence is
known as the Clay or Kinnear-Perren reaction [1, 2].
Several variations of this important reaction are
known. Instead of phosphorus trichloride other P-
nucleophiles can be used: phosphorus tribromide
leads (after hydrolysis) to alkylphosphonic dibro-
mides [3], dichlorophosphines to diorganophos-
phinic chlorides [4 - 7]. Aluminium trichloride was
successfully substituted by aluminium tribromide
[8 ], and also by anhydrous sulfuric acid [4 - 6 ,
9, 10]. Treatment of the ionic intermediate with
thiourea [1 1 ] or thiols [12 ] gives access, in certain
cases, to alkylthiophosphonic dichlorides.
TrtPCl2
1
A1C1,
t-BuCl
t-BuPClj
3
[Trt] [A1C14]
+
[PCI]
t-BuCl
A1C1,
4x
It is important that a carbocation of high stabil-
ity can be derived from the alkyl halide employed.
Accordingly, isomerization is observed in cases in
which the formation of a thermodynamically more
stable carbocation from the primary ionic interme-
diate is possible [3, 4, 13 - 15].
4 [Trt]+[A1C14] + P2C14 + |-PX
[(t-Bu)2PCl2f [AlCl4f
4
H,0
(t-Bu)2P; ci
Results
We tried to achieve the formation of a phos-
phorus-carbon bond under Kinnear-Perren condi-
Scheme 1.
This observation becomes understandable if one
takes into consideration that the P-C bond in
triphenylmethyldichlorophosphine 1 [16] is readily
* Reprint requests to R. Schmutzler.
K
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i
1266
V. Plack e t al. ■An Unusual Kinnear-Perren Reaction
cleaved upon treatment of 1 with aluminium chlo-
ride [19]. Abstraction of Cl- from 1 by the Lewis
acid aluminium trichloride, and elimination of Trt+
from 1 leaves a putative chlorophosphinidene frag-
ment (Scheme 1). In the absence of a suitable trap-
ping agent, this fragment is known to dispropor-
tionate yielding tetrachlorodiphosphine 2 and amor-
phous phosphorus Pn [19]; in the presence of tert-
butyl chloride it is readily inserted into the car-
bon-chlorine bond of the latter, yielding terr-butyl-
dichlorophosphine 3 [17] which was observed by
11P NMR spectroscopy in low concentration dur-
ing the reaction. In the following step 3 acts as
a nucleophile. It attacks the carbon center of an-
other molecule of fm-butyl chloride whose elec-
trophilicity is enhanced by complex formation with
aluminium trichloride. This leads to di-terr-butyl-
dichlorophosphonium tetrachloroaluminate 4, from
which di-te/7-butylphosphinic chloride 5 is obtained
by hydrolysis.
employed in the reaction is reduced, the formation
of tetrachlorodiphosphine 2 is always observed.
Experimental
The working conditions are described elsewhere [20],
Triphenylmethyldichlorophosphine 1 was synthesized as
previously described [16].
Reaction o f triphenylmethyldichlorophosphine 1 with
tert-butyl chloride and aluminium trichloride, followed
by hydrolysis; formation o f di-tert-butylphosphinic chlo-
ride
To a mixture of 0.772 g (5.8 mmol) of aluminium
trichloride and 0.54 g (5.8 mmol) of terf-butyl chlo-
ride was added at r. t. a solution of 1.0 g (2.9 mmol)
of triphenylmethyldichlorophosphine
1 in 10 ml of
dichloromethane. The mixture was stirred for 2 h at r. t.,
and hydrolyzed by addition of 10 ml of water. After sep-
aration of the layers, the solvent was removed from the
organic layer, and the remaining oily substance was in-
vestigated by 'H and 11P NMR spectroscopy. Di-tert-
butylphosphinic chloride 5 was identified by its NMR
parameters [17, 18],
The course of this reaction strongly depends
on the correct stoichiometry. If the amount of
tert-butyl chloride and/or aluminium trichloride
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