PROCEDE POUR LA PREPARATION DE LA N,N-DIMETHYLHYDRAZINE

PROCESS FOR PREPARING N,N-DIMETHYLHYDRAZINE

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
A method for preparing unsymmetrical dimethyl-
hydrazine wherein an acid hydrazide is first reductively
alkylated with formaldehyde and the resultant N,N-dimethyl-
2-acylhydrazine thereupon cleaved via either basic hydrolysis
or hydrazinolysis to provide the desired substituted
hydrazine.

Revendications

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:
1. A method for preparing 1,1-dimethyl hydrazine
which comprises the steps:
(a) reductively alkylating an acid hydrazide of the
formula
<IMG>
wherein R represents lower alkyl with formaldehyde
at a pH less than about 7.5 to provide the
corresponding N,N-dimethyl-2-acylhydrazine;
(b) cleaving said N,N-dimethyl-2-acylhydrazine by the
base hydrolysis or the hydrazinolysis thereof; and
(c) recovering the 1,1-dimethyl hydrazine from the
reaction mixture of step (b).
2. A process in accordance with claim 1, wherein said
acid hydrazide is acetylhydrazine and wherein said reductive
alkylation is effected at a temperature from about 20 - 100°C.
and at a pH of from about 6 - 7.
3. A process in accordance with claim 2, wherein
said acetylhydrazine and the formaldehyde are present in molar
ratio of from about 1:2::1:3, respectively, and the reaction
temperature is from about 50 - 70°C.
4. A process in accordance with claim 3, wherein the
acetylhydrazine and formaldehyde are present in the molar
ratio of 1:2.1, respectively.
19

5. A process in accordance with claim 4, wherein said
step (b) the N,N-dimethyl-2-acetylhydrazine is cleaved under
base hydrolysis conditions provided by the presence of aqueous
sodium hydroxide.
6. A process in accordance with claim 5, wherein the
molar ratio of N,N-dimethyl-2-acetylhydrazine to sodium
hydroxide is from 1:1::1:4, respectively.
7. A process in accordance with claim 6, wherein the
molar ratio of N,N-dimethyl-2-acetylhydrazine to sodium
hydroxide is about 1:2, respectively.
8. A process in accordance with claim 4, wherein said
step (b) the N,N-dimethyl-2-acetylhydrazine is cleaved by
reaction with hydrazine.
9. A process in accordance with claim 8, wherein
said hydrazine is anhydrous and is present in the amount to
provide a molar ratio of N,N-dimethyl-2-acetylhydrazine to
hydrazine of from 1:1::1:10, respectively.
10. A process in accordance with claim 9, wherein the
molar ratio of N,N-dimethyl-2-acetylhydrazine to hydrazine
is from 1:5, respectively.
11

Description

lOS~
BACKGROUND OF THE I~EMTION
Field of the Invention
This invention relates to a method for preparing
a substituted acyclic diamine.
Description of the Prior Art
Unsymmetrical dimethylhydrazine (UDMH) is a
versatile chemical intermediate having recognized usefulness
in the preparation of surfactants, insecticides, dyes, monimers,
etc The most important current use thereof, however, is
as such in the field of liquid propellants for rockets.
There presently exists two applicable commercial
methods for producing UDMH. The more desirable of these
methods, particularly from the standpoint of overall efficiency,
involves the hydrogenation of nitrosodimethylamine in turn
obtained by nitrosating dimethylamine. This method suffers
because nitrosodimethylamine has been identified as such a
powerful carcinogen that in order to provide absolute
protection for plant workers, an exceedingly expensive plant
installation is indicated. The market for UDMH, on the other
hand, is not sufficiently large enough to justify such an
expenditure.
The other method available for producing UDMH
commercially is in accordance with the Raschig process, which
is based upon the reaction of monochloramine with dimethyl-
amine. This method, while presenting tedious problems
associated with the recovery of the UDMH, poses an additional
drawback in that the preparation of monochloramine can lead
to the formation of minute quantities of trichloramine. The
latter compound is so highly explosive that extreme care must
be observed in order to assure that none of this unstable

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by-product is produced.
Accordingly, there exists an important need for
a commercially adaptable method of producing unsymmetrical
dimethylhydrazine which is not capital intensive and further-
more does not involve the formation of hazardous intermediatesor by-products. The object of this invention is to provide
such an improved method.
SUM~RY OF THE INVENTION
In accordance with the present invention a method
comprising a two-step procedure is provided for the preparation
of unsymmetrical dimethylhydrazine. In the first step of the
method an acid hydrazide is reductively alkylated with
formaldehyde resulting in the formation of the corresponding
N,N-dimethyl-2-acylhydrazine. In the second step the indicated
substituted hydrazine is cleaved by either (I) base hydrolysis
or (II) reaction with hydrazine to yield the l,l-dimethyl-
hydrazine.
The following equation is illustrative of the
underlying reactions of the method of this invention.
O CH2O/H2 O OH O
Il 11 11
RCNHNH2 ~RCNHN(CH3)2~ RC-0 + H2NN(CH3)2 (I)
Cat.
H2NNH2 O
11
~ RCNHNH2 + H2NN(CH3)2 (II)
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The acid hydrazides useful in the practice of this
invention can be conveniently derived from a lower fatty acid.
The preferred acid hydrazide is acetyl hydrazine which can
-- 2 --
,: .

lOS19~8
readily be obtained by reacting a lower ester of acetic acid,
preferably the ethyl ester, with hydrazine. The reaction is
generally carried out in a lower alcohol of which methanol is
most suitable, although solvents are not necessary for effect-
ing this reaction. The hydrazine can be anhydrous but foreconomic reasons the conventional 85% hydrazine hydrate of
commerce is preferred. The reaction temperature is desirably
that of about the boiling point of the ester employed.
Employing the preferred ethyl acetate, such temperature is in
the order of 60C. The reactants are preferably combined to
provide about a 10~ mole excess of the ester. An alcohol
solvent, when employed, is ordinarily used on a basis of about
one mole per mole of the ester. Following completion of the
reaction, the acid hydrazide solution can be used as is or
it can be stripped to remove water, alcohol, unreacted ester
or combinations thereof. While the foregoing preparation
does not form part of this invention, the working examples
will nonetheless illustrate the indicated preferred procedure
for obtaining an acid hydrazide from its corresponding fatty
acid source.
The first step of the process of this invention
consists of reductively alkylating the acid hydrazide with
formaldehyde to yield the corresponding N,N-dimethyl-2-
acylhydrazine. The formaldehyde can be in the form of an
aqueous or methanolic solution thereof although para-
formaldehyde serves as well. The preferred form of formaldehyde
is Methyl Formcel@(formaldehyde methyl hemiacetal). The
acyl hydrazine and formaldehyde can be combined in a molar
ratio of from 2 to 3 moles of the formaldehyde per mole of
the hydrazine. The preferred molar ratio of the aforesaid

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reactants is l mole of the acyl hydrazine to 2.1 moles of
formaldehyde.
A suitable temperature range for carrying out the
reductive alkylation reaction is from about room temperature
to 100C. More preferably, the reaction temperature is
maintained within the range of from about 50 to 70C. During
the reductive alkylation step hydrogen pressures between about
50 to 150 psig are generally applicable. A closed pressure
system is preferred but an open system wherein the reaction
mixture is sparged with hydrogen represents an acceptable
mode of operation if means are available for recycling
hydrogen.
The catalyst useful for effecting reductive
alkylation can be the particulate catalytic materials in the
form of a Group VIII metal such as palladium, platinum,
rhodium, nickel, cobalt and iridium. The usual supports for
such catalytic materials can be used, representative of which
include carbon, alumina, silica, silica-alumina and titania.
The preferred catalyst in the context of this invention is
palladium on a carbon support.
The reductive alkylation reaction can be carried
out in the absence of a reaction solvent; that is, in the
neat form. The use of a solvent, however, is preferred. The
solvent desirably should be a polar solvent of which the lower
alkanols and particularly methanol, represent the solvents
of choice.
An important feature of this invention resides in
the pH control of the reactants during reductive alkylation.
During the course of this reaction the pH should be maintained
at not in excess of 7.5. The preferred pH range is in the

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order of from about 6 to 7, Maintaining the pH as indicated
results in a much cleaner reaction than is otherwise obtained
and importantly contributes to realizing an essentially
quantitative yield and long catalyst life. The pH of the system
can be regulated by the addition of an appropriate amount of
a lower carboxylic acid such as, for example, acetic or formic
acid. Still another applicable pH control acid is phosphoric.
The latter acid may be most advantageously used under those
circumstances where corrosion problems associated with the use
of the indicated carboxylic acids are presented. Following
the completion of the reaction, recovery of the resultant
N,N~dimethyl-2-acyl hydrazine can be accomplished by stripping
the reaction mixture to remove volatiles. By carrying out
the reaction under the preferred conditions noted above,
essentially quantitative yields are realized.
Two displacement type procedures exist for convert-
ing the substituted acyl hydrazine to unsymmetrical dimethyl
hydrazine. Such modes include base hydrolysis and hydrazin-
olysis. Base hydrolysis represents the preferred procedure.
For this purpose, a variety of bases are applicable but the
alkali metal hydroxides represent the preferred bases, with
sodium hydroxide being the base of choice. The amount of base
can vary from 1 to 4 moles per mole of the acyl hydrazine.
An aqueous solution of the preferred base; namely, sodium
hydroxide, in the order of about 50% concentration is desirably
used. The preferred amount of the sodium hydroxide employed
in the hydrolysis reaction is about 2 moles per mole of the
acyl hydrazine. Suitable temperatures in effecting hydrolysis
range from about 60 - 100C. with a temperature in the order
of 90 - 100C. being preferred. The unsymmetrical dimethyl
-- 5 --

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hydrazine can be conveniently recovered by distillation during
the course of the reaction. The time required for effectiny
hydrolysis is in the order of several hours. Observing the
preferred conditions noted above, yields in excess of 80%
of theoretical are observed.
Another suitable method of displacing the unsymmet-
rical dimethyl hydrazine from the acyl hydrazine consists of
reacting the latter with anhydrous hydrazine. A broad
temperature range for effecting hydrazinolysis is from about
65 - 125C. The preferred temperature is in the order of
100C. An amount of hydrazine ranging from 1 to 10 moles
thereof per mole of the acyl hydrazine can be satisfactorily
used. The preferred amount, however, ranges from 1 to 5 moles
on the indicated basis. Similar to the method of recovering
unsymmetrical hydrazine employing base hydrolysis, the desired
product can be distilled during the course of displacement
reaction. Recovery yields in excess of about 70~ theoretical
can be realized in accordance with the hydrazinolysis reaction.
In order to illustrate to thoseskilled in the art
the best mode contemplated for carrying out the invention,
the following working examples are set forth. It is to be
understood that these examples are given solely by way of
illustration and accordingly, any enumeration of details set
forth therein is not to be interpreted as limiting the invention
except as such limitations appear in the appended claims. All
parts and percentages are by weight unless otherwise noted.
EXAMPLE I
Hydrazine Formation
Into a suitable reaction vessel were charged
isopropyl alcohol (8 lbs.) and 85~ hydrazine hydrate (36 lbs.).

~V5~
The mixture was heated to 40C. and ethyl acetate
(49 lbs.) was added over a 20 minute period. The temperature
climbed slowly to 60C. where it was maintained for four
hours. Following completion of the reaction, the mixture was
stripped to provide a quantitative yield of acetylhydrazine
which crystallized on cooling.
Reductive alkylation
Into a suitable pressure reactor were charged
acetyl hydrazine (41 lbs.), methanol (40 lbs.) and palladium
on carbon catalyst (3.3 lbs.). The reactor was flushed with
hydrogen and heated to 45C. and the hydrogen pressure then
raised to 100 psig. Over a period of 120 minutes a mixture of
Methyl Formcel (80 lbs.~ and acetic acid (4 lbs.) was pumped
into the reactor while maintaining the hydrogen pressure
constant at about 100 psig. The exothermic reaction was
completed about 10 minutes following the addition of the mixture
of formaldehyde and acid. The product, N,N-dimethyl acetyl-
hydrazine, was formed in essentially quantitative yield and was -
isolated by filtration of the catalysts and stripping of the
solvent. The product was a colorless liquid at room tempera-
ture.
Base Hydrolysis
The above reactor was set up for distillation
into which was charged N,N-dimethyl acetylhydrazine (56 lbs.)
which was then stirred and heated to 90C. over a period of
30 minutes. An aqueous solution of 50% sodium hydroxide
~96 lbs.) was thereupon added. An exothermic reaction occurred
and unsymmetrical dimethyl hydrazine was distilled from the
reactor. The yield of UDMH was in excess of 80% and the
purity thereof without fractionation was in the order of 91%.

~)5~
By analysis the impurities were found to be methylamine 2.2%,
methylene-dimethyl hydrazine 2.0% and water 4.7%.
Hydrazinolysis
Into a suitable reactor equipped with a distil-
lation column were charged 10.2 parts of the N,N-dimethyl
acetylhydraæine and 6.75 parts of hydrazine. The mixture was
heated to 100C. with stirring and 4.93 parts of UDMH was
distilled off. GC analysis indicated the UDMH was 96%
pure representing 74% of theoretical yield.
The pot residue was vacuum stripped and dissolved
in an acetylhydrazine mother liquor. The solution was cooled,
filtered, washed with isopropanol and dried, thus providing
acetylhydrazine for recycle.
EXAMPLE II
Into a 30-gallon reactor fitted with a reflux
condenser were charged 57.8 lbs. of ethyl acetate and 35.1 lbs.
of 85% hydrazine hydrate. With stirring the reaction mixture
was heated under reflux for ten hours and cooled. Glacial
acetic acid was added to the cooled reaction mixture until
a pH of 6 was reached, followed by the addition of 1.7 lbs.
of 50% wet power of 5% palladium on carbon. The reactor was
then sealed and pressurized to 100 psig with hydrogen.
1~ .
Methyl Formcel containing 5% acetic acid in the
amount of 57 lbs. was pumped into the reactor over a period
of five hours. Heating was applied and the temperature
maintained at 60 - 90C. and the pressure held between
100 - 150 psig during the formaldehyde addition. The reactor
was then cooled, vented and the catalyst filtered. Solvents
present in the reaction mixture (methanol, ethyl acetate,
ethanol) were distilled and recovered. The resulting aqueous

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solution of dimethyl acetyl hydrazine was then mixed with 50%
sodium hydroxide in the amount of 68 lbs. and heated carefully
at 60C. with reflux cooling. After three hours the reactor
was set up for distillation and 99% pure unsymmetrical
dimethyl hydrazine was distilled from the mixture. The
recovery of said hydrazine was in the order of about 28 lbs.