Process for making &ggr;-alkoxyamines

Details Process for making &ggr;-alkoxyamines Process for making &ggr;-alkoxyamines

1999-01-22

2004-09-21

Stockton, Laura L. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Nitriles

Reexamination Certificate

active

06794530

ABSTRACT:

This invention relates to a process for preparing &bgr;-alkoxy-nitriles by reacting low molecular weight &agr;,&bgr;-unsaturated nitrites, having up to 40 carbon atoms for example, with monohydric, dihydric or trihydric alcohols, each having a molar mass of up to 2.5×10
3
g/mol for example, in the presence of basic catalysts at from −20 to +200° C.
The 1,4-addition of monohydric or polyhydric alcohols to &agr;,&bgr;-unsaturated nitriles is a known reaction which is classified as a Michael-type addition in J. March, Advanced Organic Chemistry, 3
rd
Ed., page 665, J. Wiley & Sons, 1985, because of the reaction mechanism.
As observed in H. A. Bruson, Organic Reactions, Vol. 5, Chapt. 2, page 89, R. Adams (Ed.), J. Wiley, 1949, for example, this addition reaction usually requires a basic catalyst in order that satisfactory reaction rates may be obtained.
In many cases, the reaction mixtures comprising the 1,4-addition product are directly, without purification, converted into &ggr;-alkoxyamines in a second process step by subsequent catalytic hydrogenation. Existing processes are surveyed, for example, in Houben-Weyl, Methoden der organischen Chemie, volume 11/1, pages 341 et seq., 4th edition (1957).
Since the 1,4-addition of alcohols to &agr;,&bgr;-unsaturated nitriles to form &bgr;-alkoxynitriles is reversible, the reversal of the formation of &bgr;-alkoxynitrile must be avoided in any subsequent hydrogenation in the presence of the basic catalyst (cf. also: B. A. Bruson, Organic Reactions, Vol. 5, page 90, para 3, lines 8-11). Removal prior to the hydrogenation step of the small amounts of basic catalysts used is uneconomical, and they therefore have to be neutralized with an acid. In any subsequent catalytic hydrogenation of the &bgr;-alkoxynitrile, the hydrogenation catalyst must not be damaged by the 1,4-addition catalyst or its neutralized form.
Typical catalysts for the 1,4-addition of alcohols to &agr;,&bgr;-unsaturated nitriles include, for example, the metals sodium and potassium or their oxides, hydroxides, hydrides, cyanides and amides, as likewise observed in H. A. Bruson, Organic Reactions, Vol. 5, pages 81 and 89. The catalysts are customarily used in amounts of from 0.5 to 5% by weight, based on the alcohol.
W. P. Utermohlen, J. Am. Chem. Soc. 67, 1505-6, disclosed the use of sodium methoxide as basic catalyst.
The use of alkali metals entails appreciable problems with the handling of these reactive catalysts. Furthermore, alkali metal hydrides, amides and alkoxides are highly moisture-sensitive and industrially handleable only at great expense. And the chemical composition of these catalysts must be checked before use to determine their activity.
There has therefore been no shortage of attempts to find catalysts which are simple to handle on an industrial scale and, at the same time, are sufficiently active to enable the 1,4-addition reaction to take place with very high space-time yields.
DE-A-20 61 804 discloses that, inter alia, organic secondary or tertiary amines, for example piperidine or triethylamine, are useful as basic catalysts for the 1,4-addition of B-thio or &bgr;-sulfoxide-substituted ethanols to &agr;,&bgr;-unsaturated nitriles. However, secondary amines have only limited usefulness as catalysts, since they actually react with &agr;,&bgr;-unsaturated nitrites.
DE-A-35 22 906 discloses basic catalysts, including tertiary amines, for example triethylamine or pyridine, useful both for the preparation of 2,2′-dicyanodiethyl ether (NC—(CH
2
)
2
—O—(CH
2
)
2
—CN) from acrylonitrile and water and for the synthesis of &bgr;-alkoxynitriles from 2,2′-dicyanodiethyl ether and an alcohol.
U.S. Pat. No. 2,333,782 discloses tributylamine as catalyst for the 1,4-addition of formaldehydecyanohydrin to acrylonitrile to form &bgr;-(cyanomethoxy)propionitrile.
Basic catalysts used for the 1,4-addition of alcohols to &agr;,&bgr;-unsaturated nitriles have frequently been quaternary tetraalkylammonium hydroxides or solutions thereof, for example benzyltrimethylammonium hydroxide (a=Triton® B), for example described in U.S. Pat. No. 3,493,598 and W. P. Utermohlen, J. Am. Chem. Soc. 67, 1505-6 (1945), or tetrakis(2-hydroxyethyl)ammonium hydroxide, described for example in DE-A-21 21 325 and DE-A-22 17 494.
As is common general knowledge, tetraalkylammonium hydroxides are thermally unstable, decomposing to form a trialkylamine, alkene and water (Hofmann elimination; see for example: R. T. Morrison and R. N. Boyd, Organic Chemistry, 6th Ed., 1992, page 854 bottom to page 855 top).
Tetraalkylammonium hydroxides having from 1 to 4 &bgr;-hydroxy substituents are likewise thermally unstable, decomposing by intra- and/or intermolecular reactions (see for example: A. R. Doumaux et al., J. Org. Chem. 38, 3630-2 (1973) and A. C. Cope et al. in ‘Organic Reactions’, Vol. 11, Chapter 5, Wiley, New York, 1960).
These catalysts and their solutions therefore have only limited storage life, so that their chemical composition needs to be checked too before use to determine their activity.
Owing to their thermal lability, tetraalkylammonium hydroxides used as catalysts for the 1,4-addition of alcohols to &agr;,&bgr;-unsaturated nitrites at the customary reaction temperatures of from 35 to 140° C. (H. A. Bruson, Organic Reactions, Vol. 5, Chapt. 2, pages 89, 90 and 93) frequently give poor yields of the 1,4-addition products. Another important disadvantage is the fact that a thermally partially decomposed catalyst or its solution will cause a delay in the startup of the 1,4-addition reaction. This may cause the nitrile concentration in the reaction vessel in which the addition reaction is being carried out by addition of the &agr;,&bgr;-unsaturated nitrile, for example acrylonitrile, to the alcohol will build up to a dangerously high level and, in the extreme case, may lead to a markedly thermic polymerization of the &agr;,&bgr;-unsaturated nitrile.
Further disadvantages of quaternary ammonium hydroxides are their inutility for the 1,4-addition of polyhydric alcohols to &agr;,&bgr;-unsaturated nitrites (see DE-A-22 17 494), the fact that the 1,4-addition products frequently exhibit an undesirable discoloration, and the need to neutralize them with an acid after the 1,4-addition reaction has taken place and to remove the resulting salt if the &bgr;-alkoxynitriles are to be subjected directly to a catalytic hydrogenation to form &ggr;-alkoxyamines (see DE-A-21 36 884).
It is an object of the present invention to provide an improved process for the 1,4-addition of monohydric, dihydric or trihydric alcohols to &agr;,&bgr;-unsaturated nitrites, which does not have the above-described disadvantages and which even makes it possible for the resulting reaction:mixture of the 1,4-addition products to be converted directly in a second process step into &ggr;-alkoxyamines by hydrogenation in the presence of a hydrogenation catalyst without there being a need for any prior removal or neutralization of the catalyst for the 1,4-addition.
We have found that this object is achieved by a process for preparing &bgr;-alkoxynitriles:by reacting &agr;,&bgr;-unsaturated nitrites, having from 3 to 40 carbon atoms for example, with monohydric, dihydric or trihydric alcohols, each having a molar mass of up to 2.5×10
3
g/mol for example, in the presence of basic catalysts at from −20 to +200° C., which comprises using a diazabicyclo-alkene catalyst of the formula I
where from 1 to 4 hydrogen atoms may be independently replaced by the radicals R
1
to R
4
,
in which case R
1
, R
2
, R
3
, R
4
are each C
1-20
-alkyl, C
6-20
-aryl or C
7-20
-arylalkyl, and
n and m are each an integer from 1 to 6.
The radicals R
1
, R
2
, R
3
and R
4
independently have the following meanings:
C
1-20
-alkyl, such as methyl, ethyl, n-propyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, cyclopentyl, cyclopentylmethyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, isoheptyl, cyclohexylmethyl, n-octyl, isooctyl, n-nonyl, n-decyl, n-undecyl, n-.dodecyl, n-tridecyl, n-tetradecyl, n

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