U.S. patent application number 10/202996 was filed with the patent office on 2003-08-21 for process for the preparation of pure aryllithium compounds and their use.
Invention is credited to Dawidowski, Dirk, Emmel, Ute, Weiss, Wilfried, Wietelmann, Ulrich.
Application Number | 20030155665 10/202996 |
Document ID | / |
Family ID | 7699587 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030155665 |
Kind Code |
A1 |
Emmel, Ute ; et al. |
August 21, 2003 |
Process for the preparation of pure aryllithium compounds and their
use
Abstract
A process is described for preparing aryllithium compounds by
reaction of metallic lithium in an ether-containing solvent with an
aryl halide, wherein prior to or at the beginning of the reaction a
catalyst is added, the catalyst containing a halogen-free,
polynuclear aromatic (aryl catalyst) or consisting of such a
compound.
Inventors: |
Emmel, Ute; (Frankfurt am
Main, DE) ; Weiss, Wilfried; (Oberursel, DE) ;
Wietelmann, Ulrich; (Friedrichsdorf, DE) ;
Dawidowski, Dirk; (Frankfurt, DE) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI, LLP
666 FIFTH AVE
NEW YORK
NY
10103-3198
US
|
Family ID: |
7699587 |
Appl. No.: |
10/202996 |
Filed: |
July 22, 2002 |
Current U.S.
Class: |
260/665R |
Current CPC
Class: |
C07F 1/02 20130101 |
Class at
Publication: |
260/665.00R |
International
Class: |
C07F 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2001 |
DE |
101 46 233.6 |
Claims
1. Process for the preparation of aryllithium compounds by the
reaction of metallic lithium in an ether-containing solvent with an
aryl halide, characterised in that, prior to or at the beginning of
the reaction, a catalyst is added, the catalyst containing a
halogen-free, polynuclear aromatic (aryl catalyst) or consisting of
such a compound.
2. Process according to claim 1, characterised in that the aryl
catalyst used is a polynuclear, halogen-free aromatic selected from
the group of ortho-condensed aromatics or from the group of
aromatics bonded to one another by single bonds, the aromatic
possibly being alkyl-substituted or possibly containing a
functional group.
3. Process according to claim 2, characterised in that naphthalene,
phenanthrene, anthracene, diphenyl or 4,4'-di-tert. butyldiphenyl
is used as the aryl catalyst.
4. Process according to one of claims 1 to 3, characterised in that
the aryl catalyst is added in a quantity of 0.05 to 2 mol. % (based
on the total quantity of aryl halide used).
5. Process according to one of claims 1 to 4, characterised in that
the metallic lithium is in finely-divided form, having particle
sizes of <0.1 mm, and is dispersed in the solvent.
6. Process according to one of claims 1 to 5, characterised in that
the lithium metal has an Na content of 0.5 to 5 wt. %.
7. Process according to one of claims 1 to 6, characterised in that
an excess of 1 to 40 mol. % lithium to aryl halide is used.
8. Process according to one of claims 1 to 7, characterised in that
acyclic ethers R--O--R' where R and R' independently of one another
each have 1 to 6 C atoms, or cyclic ethers having 4 to 8 C atoms,
individually or in a mixture, are used as the ether-containing
solvent.
9. Process according to one of claims 1 to 8, characterised in that
diethyl ether, dipropyl ether, dibutyl ether, tert. butyl methyl
ether, tert. amyl methyl ether, tetrahydrofuran,
2-methyltetrahydrofuran or tetrahydropyran, individually or in a
mixture, is used as the ether-containing solvent.
10. Process according to one of claims 1 to 9, characterised in
that the ether-containing solvent contains, in addition, anhydrous
hydrocarbons in a quantity of 50 wt. % at most, based on the total
quantity of solvent.
11. Process according to one of claims 1 to 10, characterised in
that a drying agent is added to the lithium metal suspension prior
to the addition of the aryl halide.
12. Process according to one of claims 1 to 11, characterised in
that the temperature of the reaction (addition stage and
post-reaction stage) is -20.degree. C. to +100.degree. C.
13. Process according to one of claims 1 to 12, characterised in
that the aryl halide used is a halobenzene and the ether-containing
solvent used is dibutyl ether and that phenyllithium is obtained as
product.
14. Process according to claim 13, characterised in that the
ether-containing solvent contains another ether in addition to
dibutyl ether.
15. Process according to one of claims 1 to 12, characterised in
that the aryl halide used is a halobenzene and the ether-containing
solvent used is dibutyl ether in a mixture with cyclohexane or
methylcyclohexane and that phenyllithium is obtained as
product.
16. Use of the aryllithium compounds prepared by a process
according to one of claims 1 to 15 as reagents in organic
synthesis.
Description
[0001] This invention relates to a process for the preparation of
pure aryllithium compounds and their use.
[0002] The preparation of aryllithium compounds in organic solvents
by reacting aryl halides with lithium metal has been known for a
long time. Because aryllithium compounds are usually insoluble in
hydrocarbons, preferred organic solvents are ethereal solvents, for
example, diethyl ether. However, solutions of aryllithium compounds
in pure diethyl ether are not usually sufficiently stable on
storage. For this reason, solutions of aryllithium compounds in
ether-containing solvents having a restricted ether content have
been developed. Aryllithium compounds decompose more slowly in
these solutions. Thus U.S. Pat. No. 3,197,516 and U.S. Pat. No.
3,446,860 describe solutions of phenyllithium in diethyl
ether/hydrocarbon mixtures. Such solutions have the disadvantages
that they are only a moderate improvement as regards their heat
stability and that they have to be stored in cold conditions
(0.degree. C. to 5.degree. C.). Even at these temperatures a
discoloration is to be observed after relatively prolonged storage,
and phenyllithium/ether complexes frequently precipitate out in
crystalline form.
[0003] Better, i.e. stabler, products can be obtained by using
higher ethers. Thus WO 92/19622 describes a process for preparing
solutions of aryllithium compounds in ethereal solvents ROR' where
R, R', independently of one another, are alkyl groups having 3 to 8
C atoms. With the use of dibutyl ether, for example, 5% to 25%
phenyllithium solutions which are stable for three weeks at
40.degree. C. are obtained. Disadvantages of this process, however,
are yields which do not reproduce and the inferior purity of the
resulting products. An example giving a very high yield (96%) and
extremely high product purity (>99%) is described in WO
92/19622, but these data could not be reproduced.
[0004] Thus, in U.S. Pat. No. 5,626,798 (the same applicant as the
applicant of WO 92/19622) there is the criticism that product
solutions in which dibutyl ether is used as solvent are in fact
stabler, but that difficulties arose owing to the decreased Lewis
basicity of the solvent employed. Thus the rate of the reaction
between lithium metal and chlorobenzene decreased during the final
quarter of the halide addition. Owing to this retarding of the
reaction, impurities such as diphenyllithium and diphenyl were
formed as a result of secondary reactions between phenyllithium and
chlorobenzene. This led inevitably to a decrease in the
phenyllithium content during storage. These observations could be
confirmed in experiments by the present writers (see Comparison
Example B).
[0005] In order to increase the reaction rate, U.S. Pat. No.
5,626,798 recommends the addition of certain Lewis bases
corresponding to the formula R.sup.2AR.sup.3(R.sup.4) or of cyclic
compounds (CR.sup.5R.sup.6).sub.yA(R.sup.4).sub.z, wherein A is
selected from oxygen, nitrogen, phosphorus or sulfur; R.sup.2,
R.sup.3 and R.sup.4 are selected from alkyl groups having 1 to 6 C
atoms; R.sup.5 and R.sup.6 are independently selected from hydrogen
or alkyl groups containing up to 6 C atoms; y is an integer between
4 and 6; if A is oxygen or sulfur, z is equal to zero and if A is
nitrogen or phosphorus, z is equal to 1. Here the molar ratio of
ether to aryl halide is at least 1.3 to 1 and the molar ratio of
Lewis base to aryl halide is 0.01 to 0.50.
[0006] Disadvantages of this process are the still unsatisfactory
yields of 87.4% to 91.5% (see the three examples described in U.S.
Pat. No. 5,626,798), but above all the decreased stability on
storage. U.S. Pat. No. 5,626,798 gives no details regarding this,
but in comparison examples by the present writers it was shown that
solutions which contain the required Lewis bases, in particular
MTBE (methyl tert. butyl ether), decompose considerably more
rapidly than do those without the above-mentioned additives (see
the present Examples, Table 1). The cause of this is an attack of
the aryllithium compounds on the Lewis bases, presumably
accompanied by splitting of the C--O-- bonds. In this way,
black-coloured solutions having a distinctly increased residual
base content are formed. Moreover, the product solutions prepared
as in U.S. Pat. No. 5,626,798 still have a relatively high aryl
halide content. Thus, the product described as Example 1 has a
chlorobenzene content of 1 wt. % (corresponding to 3.3 mol. %),
which is indeed reduced in comparison with prior art, but is still
very high. The diphenyl content is also still unsatisfactorily high
(see the present Comparison Example A, Table 3).
[0007] The object of the present invention is to avoid the
disadvantages of the prior art and to demonstrate a process for the
preparation of aryllithium compounds which avoids the slowing down
of the rate of the reaction between aryl halide and lithium metal
(in particular in the final quarter of the aryl halide addition)
and delivers a pure product having a high yield (for example
>90%). By product purity is meant in particular a decreased
content of coupling products (for example, diphenyl), aryl halides
and residual base (formation as a result of attack on Lewis bases
having high Lewis basicity).
[0008] The object is achieved by a process for the preparation of
aryllithium compounds, in which metallic lithium, which is
preferably in the form of a dispersion, in an ether-containing
solvent is reacted with an aryl halide and a catalyst is added
prior to or at the beginning of the reaction, the catalyst
containing a halogen-free, polynuclear aromatic (aryl catalyst) or
consisting of such a compound.
[0009] Surprisingly, it has been found that halogen-free,
polynuclear aromatics accelerate the reaction and at the same time
improve the selectivity, i.e. under otherwise comparable reaction
conditions, a product solution prepared according to the invention
will be significantly purer than a product prepared according to
prior art. In particular, the residual contents of aryl halide and
Wurtz secondary products are decreased.
[0010] The aryl catalyst is added prior to the beginning or at the
beginning of the reaction. In this connection, the definition of
"at the beginning" is that the addition of the aryl catalyst is
terminated when half the total quantity of the aryl halide to be
introduced has been added to the reaction.
[0011] The aryl catalyst used may be a polynuclear, halogen-free
aromatic selected from the group of ortho-condensed aromatics or
from the group of aromatics bonded to one another by single bonds;
the aromatic may be alkyl-substituted. Examples of such catalysts
are given below: 1
[0012] Suitable aryl catalysts are, in particular, the Wurtz
coupling products formed during the reaction. In this case the
preparation process is clearly optimised, without the admixture of
a foreign substance. In some cases, in particular if the given
coupling product is not commercially available, it may be
appropriate to use another aryl catalyst.
[0013] For example, ortho-condensed, polycyclic aromatics such as
naphthalene, phenanthrene, anthracene et cetera, which may be
singly or multiply alkyl-substituted, may be used. In addition,
aromatic systems bonded by single bonds, such as diphenyl,
4,4'-di-tert. butyldiphenyl, dinaphthyl et cetera, may also be
used.
[0014] The optimal quantity of aryl catalyst has to be tried out in
individual cases. It is determined by the "activity" of the
catalyst, i.e. especially by the rate of formation and stability of
the radical anion formed with lithium metal and of the solvent/aryl
halide combination. Thus, for example, in the preparation of
phenyllithium solutions in aliphatic ethers R--O--R' where R, R'
are alkyl groups having at least 3 C atoms, preferably 0.1 to 0.6
mol. % (based on the quantity of aryl halide used) of a binuclear
aromatic bonded by a single bond, for example, diphenyl or
4,4'-di-tert. butyl diphenyl, is added. As a rule, the required
quantity of catalyst is between 0.05 and 2 mol. %, based on the
total quantity of aryl halide used in each case.
[0015] Preferably the metallic lithium is in finely-divided form,
with the particle sizes being preferably <0.1 mm and
particularly preferably <0.05 mm. Preferably the lithium metal
has an Na content of 0.5 to 5 wt. %, particularly preferably 1 to 3
wt. %. Preferably an excess of lithium to aryl halide is used. The
excess is preferably 1 to 40 mol. %, particularly preferably 5 to
25 mol. %.
[0016] The solvents used are ethers, either in pure form or in a
mixture with hydrocarbons. The ethers may be acyclic or cyclic.
Acyclic ethers R--O--R' where R and R', independently of one
another, are C.sub.1 to C.sub.6 may also be used in a mixture or
together with cyclic ethers (preferably having 4 to 8 C atoms).
Preferred ethereal solvents are: diethyl ether, dipropyl ether,
dibutyl ether, tert. butyl methyl ether (MTBE), tert. amyl methyl
ether, tetrahydrofuran, 2-methyltetrahydrofuran and
tetrahydropyran. Dibutyl ether and diethyl ether are most
preferred.
[0017] Besides ethers, the ethereal solvent may also contain
anhydrous hydrocarbons in a quantity of 50 wt. % at most, based on
the total quantity of solvent. Suitable hydrocarbons are alkanes
having 5 to 8 C atoms, for example, pentane, hexane, heptane,
octane, cyclohexane or methylcyclohexane. In addition, liquid
aromatics having up to 8 C atoms, for example, benzene, toluene,
ethylbenzene and xylenes, may also be used. Cyclohexane,
methylcyclohexane and toluene are particularly preferred.
[0018] The process according to the invention is generally suitable
for the preparation of lithiated mononuclear or polynuclear
aromatics or heteroaromatics. The respective aromatics may also
carry 1 to 3 substituents. Such substituents may be selected, for
example, from the following groups: alkyl (R having 1 to 10 C
atoms), phenyl (C.sub.6H.sub.5-), tolyl (C.sub.7H.sub.8-), alkoxy
(R--O-- where R is an alkyl group having 1 to 10 C atoms),
dialkylamino (RR'N, where R and R', independently of one another,
are alkyl groups having 1 to 10 C atoms) and F.sup.-
(fluorine).
[0019] Examples of mononuclear aryllithium compounds are:
phenyllithium, 2-, 3- or 4-tolyllithium, cumyllithium,
4-dimethylaminophenyllithium, 2-lithioanisole, 2-, 3- or
4-fluorophenyllithium or fluorotoyllithium.
[0020] Examples of polynuclear aryllithium compounds are:
.alpha.-naphthyllithium, .beta.-naphthyllithium, anthracenyllithium
or phenanthrenyllithium.
[0021] Examples of heteroaromatics are 2- and 3-thienyllithium and
2- and 3-furanyllithium. 2
[0022] R.sup.1, R.sup.2, R.sup.3=independently of one another H,
alkyl group having 1 to 10 C atoms, phenyl, toluene, F
[0023] FG=functional groups such as OR.sup.1, NR.sup.1R.sup.2
[0024] x=O, S, Te, NR.sup.1
[0025] Aryl halides Ar-Hal wherein Hal=Cl, Br or I are used as
starting compounds. The chlorine compounds (for example,
chlorobenzene) are particularly preferred, as these are generally
the most readily available and are cheap and form Wurtz secondary
products the least. The commercially available halides do not
usually require further preliminary treatment. Should they be
contaminated with water or hydrogen halide (H-Hal), however, it is
recommended that an ordinary purification step, for example,
filtration through a molecular sieve, be carried out. Preferably a
drying agent, such as lithium hydride or final product solution, is
added to the lithium metal suspension prior to the addition of the
aryl halide. The addition of the aryl halide takes preferably 5
minutes to 5 hours, particularly preferably 30 to 180 minutes. The
temperature of the reaction (addition stage and post-reaction
stage) is preferably -20.degree. C. to +100.degree. C.,
particularly preferably 0.degree. C. to 60.degree. C.
[0026] The process according to the invention may be carried out,
for example, as follows:
[0027] The required anhydrous, aprotic solvent is placed in a dry
reaction vessel which has been rendered inert (i.e. filled with
protective gas such as argon or nitrogen) and finely-divided
lithium metal is added thereto. The lithium metal is generally used
in the form of powder, i.e. having particle sizes <0.1 mm,
preferably <0.05 mm. In the case of certain solvent/product
combinations, coarser lithium metal, for example, granular material
having a diameter of approximately 1 to 3 mm, may also be used. It
is particularly advantageous to use a quality of lithium having a
relatively high sodium content of 0.5 to 5 wt. %, particularly
preferably 1 to 3 wt. %. The quantity of lithium corresponds to at
least the stoichiometric quantity, i.e. twice the molar quantity,
of the subsequently added aryl halide. The lithium is preferably
used in excess, i.e. in 1 to 40 mol. % excess, particularly
preferably in 5 to 25 mol. % excess.
[0028] The halogen-free, polynuclear aryl catalyst is then added
and stirred for 5 to 100 minutes at 0.degree. C. to 60.degree. C.
In particular, if the raw materials used have been imperfectly
pretreated, i.e. are not quite free of water and other protic
contaminants, it is recommended that the reaction mixture be
activated. To that end, a small quantity of a non-interfering
drying agent (for example, lithium hydride in quantities of
approximately 0.1 to 10 g/kg solvent) is added and stirred for a
few minutes to several hours. Alternatively, final product solution
from a previous batch (for example, 0.1 to 50 ml/kg solvent) may
also be added. The Ar-Li contained in the product solution reacts
with the interfering contaminants with the resulting formation of
an "inert reaction mixture", which readily reacts with the aryl
halide added in the following step. It is also particularly elegant
to add at the "start" of a batch, or to introduce beforehand, a
solution of the Ar-Li end product containing the aryl catalyst.
[0029] The reaction mixture, thus preconditioned, is now brought to
the required reaction temperature which, depending on the
solvent/halide combination, may be a temperature between
-20.degree. C. and 100.degree. C., preferably 0.degree. C. and
60.degree. C. In the case where Ar is phenyl, the particularly
preferred reaction temperature is between 20.degree. C. and
45.degree. C. The aryl halide may be introduced in pure form or
dissolved, preferably in the same solvent as that already used for
the preparation of the Li metal suspension. In the case of liquid
aryl halides, it is preferable to use these undiluted.
[0030] The halide is added over a period typically of 5 minutes to
5 hours, preferably 30 to 180 minutes. In the course of this, the
metal suspension is stirred vigorously. The start of the reaction
between aryl halide and metal can be easily discerned from the rise
in temperature (heat of reaction) and from the formation of the
insoluble lithium halide secondary products. In order to maintain
the required temperature, the reaction is countercooled from
outside.
[0031] On conclusion of the addition, stirring is continued for at
least as long as liberated heat of reaction is observed. This is
generally the case for 10 minutes to 4 hours. On the laboratory
scale, stirring is frequently carried out overnight. The finally
reacted reaction suspension is then worked up in known manner, i.e.
it is usually filtered. A solution of the respective aryllithium
compound in an ether-containing solvent is obtained.
[0032] The halide content of the aryllithium compounds obtained,
which is decreased as a result of the process according to the
invention, leads to products which are more stable in storage,
because the Wurtz secondary reaction corresponding to
Ar-Li+Ar-Hal.fwdarw.Ar-Ar+LiHal
[0033] in the final product solution is greatly diminished or
prevented. The formation of Wurtz secondary product also takes
place during the product synthesis, the extent of the secondary
reaction being dependent on the nature of the solvent, of the
halide, of the temperature and also in particular on the quality
(i.e. activity, specific surface) and quantity (stoichiometric
quantity or excess) of the lithium used. Unexpectedly, as a result
of the addition according to the invention of the catalysts, in
particular of the Wurtz coupling product Ar-Ar which is inevitably
formed in certain quantities, the total content of this secondary
product observed at the end of the reaction can be greatly
decreased, i.e. in the product solutions prepared according to the
invention, the sum of externally added Wurtz product Ar-Ar and that
which is formed as secondary product is lower than is the case of
products prepared according to prior art.
[0034] The process according to the invention also has the
advantage that good reaction yields and short reaction times can be
achieved simultaneously, without the need for the presence of Lewis
bases, which hitherto have been thought necessary. The product
solutions containing no Lewis bases are generally more stable. This
is seen in Table 1, which shows the decomposition rates of
approximately 15% phenyllithium solutions in pure dibutyl ether and
in a mixed solvent which contains, besides dibutyl ether, 7 mol. %
methyl tert. butyl ether (MTBE, based on phenyllithium contained).
To that end, the two solutions prepared by the process according to
the invention were stored for eight weeks at 20.degree. C. to
40.degree. C. in tightly sealed glass vessels.
1TABLE 1 Decomposition rates of phenyllithium in dibutyl ether (in
% active base/day) at 20.degree. C. at 40.degree. C. without MTBE
-0.019 -0.079 with 7 mol. % MTBE -0.269 -0.337
[0035] The solution containing added MTBE had moreover turned
black, whereas the product containing exclusively dibutyl ether as
solvent remained light brownish.
[0036] The invention is explained in more detail below by means of
Examples.
EXAMPLE 1
Preparation of Phenyllithium in Dibutyl Ether, Catalyst 0.6 Mol. %
Diphenyl
[0037] 11.5 g lithium powder (1657 mmol, particle size <0.1 mm,
Na content=2.3 wt. %) and 0.17 g (19 mmol) finely ground lithium
hydride in 160 g anhydrous dibutyl ether were placed in an inerted
500 ml double-jacketed glass reactor equipped with anchor stirrer,
reflux condenser and internal thermometer and were heated to
32.50.degree. C., with stirring. Then 0.67 g (4.3 mmol) diphenyl
(>99%, Merck Schuchardt firm) was added and the whole was
stirred for 10 minutes. A mixture of 77.5 g (688 mmol)
chlorobenzene and 4.2 g (48 mmol) tert. butyl methyl ether (MTBE)
was added, dropwise, at an even rate over a period of 4 hours by
means of a dosing device. The reaction started almost immediately;
this was discernible from a rise in the internal temperature by
2.degree. C. The internal temperature was maintained within the
range of 32.degree. C. and 35.degree. C. by countercooling.
[0038] Immediately on conclusion of the addition, a sample was
withdrawn and filtered clear by means of a spray filter. A
conversion of 86% was ascertained by total base titration; a
chlorobenzene content of 4 wt. % was detected by gas chromatography
(GC).
[0039] After a two-hour post-reaction stage at approximately
32.degree. C., no further heat of reaction was detectable. The
reaction mixture was cooled to 20.degree. C. and filtered through a
fritted-glass filter and analysed:
2 Total base: 3.009 mmol/g (corresponds to 97.4% conversion)
Residual base: 0.25 mmol/g Active base: 2.759 mmol/g (corresponds
to 23.2% phenyllithium) GC analysis after hydrolysis: Diphenyl: 0.8
wt. % Chlorobenzene: 0.4 wt. % Benzene: 23.2 wt. % MTBE: 1.8 wt. %
Dibutyl ether: 72.6 wt. %
[0040] The diphenyl content of 0.8 wt. % corresponds to a content
of 2.0 mol. % based on phenyllithium.
EXAMPLES 2 to 9 and Comparative Examples A to D
Preparation of Aryllithium Compounds (Ar-Li) in Ethereal Solvents,
With and Without Catalyst
[0041] Further examples of the reaction were carried out in a
laboratory calorimeter under varied reaction conditions. This
organisation of the experiments allows the precise observation of
the liberated heat of reaction and hence, indirectly, the
determination of the reaction rate and of the so-called "thermal
degree of conversion". The thermal degree of conversion, a
dimensionless number, is found by division of the heat liberated up
to a given time by the total (on complete conversion) heat
liberated. It thus corresponds to the progress of the respective
reaction.
[0042] The further Examples 2 to 9 according to the invention were
carried out similarly to Example 1, and the individual variables
may be found in Table 2. The Comparison Examples A to D
corresponding to prior art were carried out under otherwise
identical reaction conditions, without the addition of a catalyst.
The individual variables may be found in Table 2. All the Examples
reported in Table 2 were carried out, like Example 1, using a 20
mol. % excess of lithium.
3TABLE 2 Examples 2 to 9, Comparison Examples A to D, Preparation
of aryllithium compounds (Ar--Li) in ethereal solvents Post-
thermal Con- Yield reac- degree of version Con- (incl. Dosing tion
React. Sol- Cata- conversion at End of version washing) Ex.
Ar--Li.sup.1) time time temp. MTBE.sup.2) vent.sup.3) lyst.sup.4)
end of dosing dosing filtrate (%) 2 Ph 1 3 32-38 7 Bu.sub.2O 0.6 DP
82 n.d. 97.2 95.1 A Ph 1 4 32-38 7 Bu.sub.2O J. 65 n.d. 89.6 85.0 3
Ph 1 2 32-38 J. Bu.sub.2O 0.3 DP 83 72.9 97.0 94.0 B Ph 1 4 32-38
J. Bu.sub.2O J. 73 63.0 91.3 90.8 4 Ph 1 3.5 32-38 J. Bu.sub.2O 0.1
N 72 65.9 95.6 92.5 5 Ph 1 4 32-38 J. Bu.sub.2O 0.3 69.7 61.5 93.4
92.3 TBDP 6 Ph 2 3 20-23 J. Et.sub.2O/ 0.1 DP 85.6 76.8 98.0 95.4
CH 7 Ph 2 3 20-23 J. Et.sub.2O/ 0.3 DP 88 80.7 93.6 88 CH 8 Ph 2 3
20-23 J. Et.sub.2O/ 0.5 DP 89 80 97.3 92.9 CH C Ph 2 4 20-23 J.
Et.sub.2O/ J. 82.6 57.9 84.1 79.5 CH 9 p-Tol 2 2.5 20-23 J.
Bu.sub.2O 0.3 DP 84.4 78.6 95.2 93.2 D p-Tol 2 2.5 20-23 J.
Bu.sub.2O J. 86.9 75.0 94.8 89.6 .sup.1)Ph = phenyl p-Tol = p-tolyl
.sup.2)MTBE = tert. butyl methyl ether .sup.3)Bu.sub.2O = dibutyl
ether Et.sub.2O/CH = mixture of 35% diethyl ether, 65% cyclohexane
.sup.4)DP = diphenyl N = naphthalene TBDP = di-tert. butyldiphenyl
n.d. = not determined
[0043] The reaction-accelerating and yield-enhancing effect of the
addition according to the invention of the aryl catalysts may be
inferred from Examples 2 to 9 and the corresponding Comparative
Examples A to D.
[0044] Example 2 and Comparative Example A describe the synthesis
of phenyllithium in a mixture of dibutyl ether with 7 mol. % MTBE
at a reaction temperature of between 32.degree. C. and 38.degree.
C. At the end of the dosing time, 1 hour in each case, in the
Example according to the invention 82% of the total heat of
reaction had already been liberated, whereas without a catalyst
only 65% of the heat was released. The yield in Example 2 is
approximately 99%, which is almost 10% more than in Comparative
Example A.
[0045] Similar effects also occur at half the catalyst
concentration and in the absence of the Lewis base MTBE (Example 3
and Comparative Example B).
[0046] Example 4 demonstrates that naphthalene also, even at a very
low concentration of 0.1 mol. %, brings about a rise in conversion
and in yield of approximately 3% more than in Comparative Example
B.
[0047] The addition according to the invention of the catalyst
di-tert. butyldiphenyl does not lead to an acceleration of the
reaction, but to an increase in conversion and in yield (Example 5
compared with Comparative Example B).
[0048] Examples 6 to 8 and Comparative Example C show that in a
mixed solvent consisting of 35 parts by weight diethyl ether and
65% cyclohexane, the addition according to the invention of the
aryl catalyst diphenyl likewise has a positive effect: yields and
conversions are significantly improved relative to those in
Comparative Example C. Particularly striking, too, is the
considerably higher reaction rate, which can be deduced from the
different conversions at the time of the added reagent.
[0049] Example 9 and Comparative Example D show the preparation of
p-tolyllithium in dibutyl ether. For a relatively long dosing time
of two hours, in Example 9 the thermal conversion at the end of
dosing is somewhat less than in Comparative Example D, but the
conversions and the product yield are significantly higher in the
Example according to the invention.
[0050] Samples of the clear-filtered end products obtained from the
Examples and Comparative Examples listed in Table 2 were withdrawn
and their compositions analysed by gas chromatography. The results
are shown in Table 3.
4TABLE 3 Compositions of the clear-filtered products from Table 2
Chlorobenzene Diphenyl Phenyllithium Diphenyl Example (wt. %) (wt.
%) (wt. %) (mol. %) 2 0.24 0.93 25.1 2.0 A 1.6 2.9 21.2 6.9 3 0.4
0.8 24.0 2.2 B 1.3 1.1 23.4 3.1 6 0.6 0.9 23.9 2.4 7 0.2 0.5 22.8
1.4 8 0.9 0.8 23.7 2.2 C 4.5 0.9 20.9 2.8 *based on
phenyllithium
[0051] It can be seen from Table 3 that the products prepared by
the process according to the invention have a higher purity than do
the products prepared according to prior art and are obtained in
higher yield. Thus, for example, a decrease of 85% in the
chlorobenzene content and of 70% in the diphenyl content is
established from a comparison of Example 2 and Comparative Example
A.
* * * * *