Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to the preparation of
haloalkyl phosphonic acids, especially the preparation of
2-chloroethyl-phosphonic acid (hereinafter CEPA) and more
particularly to an improved high temperature, high pressure
process for converting or cleaving bis- (2-chloroethyl~-2-
chloroethyl phosphonate (hereinafter BICEP) and/or mono-
(2-chloroethyl)-2-chloroethylphosphonate (hereinafter
MEPHA) into CEPA.
CEPA is well known to be a valuable plant hormone
producer and regulator having uses similar to ethylene as a
plant growth regulant, which uses are widely published in
the literature and reference texts, e.g., see ET~LENE IN
PLANT BIOLOCY by F.B. Ables, Academic Press, 1973.
Accordingly, CEPA is highly useful for hastening maturation
and increasing crop yields of many fruits and vegetables,
including for example soybeans, pineapples, bananas,
cherries, apples, peaches, pears, oranges, lemons, peas,
beans and tomatoes, as well as plant regulant uses
; disclosed in U.S. patent 3,879,188 and has been found to
increase yields of latex from rubber trees and the like (J.
Rubber Research Institute of Malaya, Vol. 20, part 5, pp
292-305, 1968)D Many uses of CEPA have been amply
described in the patent, trade and scientific literature,
an early such publication by Cooke and Randall (a
~5 coinventor herein) appearing in Nature, Vol. 218, p.974,
1968. The corresponding fluoro, bromo and iodo derivatives
- of CEPA also have effects on plant life as disclosed in
U.S. Patent 3,879,188. Instant products are also useful
flame retardants as disclosed in U~S. Patent 3,370,029.
Many known procedures for preparing CEPA have
generally not been entirely satisfactory from the
standpoint of economy~ efficiency, and/or product purity
and/or yield. One known procedure involves conversion of
tris-(2-chloroethyl) phosphite to BICEP and to CEPA with
aqueous HCl under about atmospheric pressure (see Akademiya
Nauk SSR Izvestiya, Otdelenie Khim, Nauk, 1946, pages 403-
410). The yields and product purity from this process are
too low for it to be considered commercially useful.
Still another method described in Randall et al
U.S. 3,787,486 involves conducting the reaction between
BICEP and excess concentrated HCl under autogenous pressure
in a sealed pressure reactor. This method results in
gr~atly improved yields and product purity; however, the
extended reaction time employed has somewhat restricted its
use as a commercial process. Also, since the excess HCl
reactant, which aids in inhibiting formation of 2-
hydroxyethylphosphonic acid (hereafter ~EPHA), is charged
as aqueous acid into the reactor at the start of the
; 20 reaction, a comparatively large volume of water in
inherently present, leading to some inefficiency in the
size of the reactor and the need for acid resistant
separating equipment for recovery of substantially pure
product.
Another improved method described in Randall et
al., U.S. 3,808,265 involves incremental addition into a
pressure-tight reactor containing BICEP, preferably in the
presence of aqueous HCl of at least 23% concentration and
at least 2 moles of water per mole of BICEP and at a
temperature of about 100 to 145C., of sufficient HCl gas
--2--
to maintain in said xeactor a super atmospheric pressure
preferably ranging from about 50 to 90 psig. The illus-
trative examples therein describe reactions carried out at
120C. and pressures of 90 psig or less and indicate that
as the ratio of aqueous HCl to BICEP decreases (the molar
ratio of water to ~IC~P decreasing from 12.5:1 to 3.5:1),
the reaction time increases so that completion of the
reaction requires a comparatively long time, which, as
pointed out above, i5 objectionable from a commercial
: standpoint.
In Randall et al U.S. 3,600,435, a method is
described involving reaction of BICEP with anhydrous ~Cl
gas at temperatures above the 140C. and atmospheric
pressures. Although this method inhibits or avoids the
production of HEPHA (from hydrolysis of C3PA), it yields/
in addition to the desired CEPA, substantial amounts of the
bix-(2-chloroethyl-phosphonic acid) anhydride (CEPAA),
thus, somewhat diluting the strength of the desired acid.
In German Patent 2,061,610 and Additions thereof,
2,134,346 and 2,148j549, processess are disclosed involving
reaction of BICEP with HCl gas at temperatures up to
200C., and pressures of 1 to 10, preferably 3 to 6,
atmospheres in the presence of 0.1 to 31% of water,
optionally in the form of aqueous HCl acid, but in all such
processes the reactor is continuously, or repeatedly,
vented to distill off the ethylene dichloride by-productr
with simultaneous drop is pressure and temperature which
must thus each time be raised again with addition HCl gas
and heat. The expense of acid resistant distillation and
reactor equipment, including control valves and the like,
prohibits its general adoption as a commercial process.
--3--
;7~
And in Dutch Patent Application 71/16982, an anhydrous process
~s disclosed involving reaction of BICEP with anhydrous HCl gas at
temperatures of lQO ~o 2Q0C. and excess pressures of 2 to 25, preferably ~-
6 to 20, atmospheres. It has been determined that such a process obtains
relatively low yields and produces an unduly darker colored CEPA product
~hich~ when employed in a formulation containing 24.5% CEPA, 32% propylene
glycol and 43.5% water for use on crops, results in a dark colored product
containing a considerable ~mount o black precipitate and a dark oily ;;
laye~
It ~ould be advantageous to have an improved process for producing
CEPA which obviates one or more of the above disadvantages; e.g. a process
~nv~lving ~eaction of BIC~P and/or MEPHA with hydrogen chloride. It would
~lso be advantageous to have a process enabling larger batch sizes ~without
~ncrease or reactor size) and/or shorter reaction times and/or higher
CEPA assays or purities and/or reducted im~urities therein. It would be
~u~ther advantageous to have a highly selective and economical process for
the pToduction of CEPA, or corresponding haloalkyl phosphonic acids, in
high yield~
The present invention provides in a process for the preparation
2Q of haloalkyl phosphonic acid, especially 2~chloroethylphosphonic acid,
~herein hydrogen halide, preferably hydrogen chloride, is contacted at
a temperature of between about 110C and about 160C with a haloalkyl~
phosphonate of the formula
11~,, OR
X(C~l21n~P
O (CH2) nX
,~
L ~ 4~
wherein X is a halogen such as fluorine, chlorine, bromine or iodine;
R is h~drogen or -CCH2)nX and n is an integer of 1 to 6, preferably X is
Cl and n is 2, the improvement which comprises conducting the reaction in
a pres~ure~tight reactor in a closed system in the presence of from about
0~1 to 1,8 moles of water per mole of said phosphonate; controlling the
water concentration within said range throughout the reaction; incrementally
adding suficient dry hydrogen halide into said pressure-tight reactor
containing the reaction mixture to ma;ntain a pressure of at least 100 psig
therein during at least a major portion of the reaction and conducting the
reaction in the absence of venting any of the contents of the reactor
during reaction. Completion of the reaction results in a liquid mixture
comp~ising primarily the corresponding alkyl dihalide and the haloalkyl-
phosphonic acid, prefera~ly ethylene dichloride and 2~chloroethylphosphonic
acid,
; Advantage~ of the present process, relative to presently employed ~,~
proces~es, generally include:
Cl~ Larger batch sizes because less aqueous HCl is introduced
or is present in the reactor.
C2l CEPA purities of 90% or more.
C3) Less by~product HEP~
C4) Less unreacted MEPHA~
(5~ Shorter reaction time cycles~
(61 Shorter stripping time because less water
is present.
(71 Lighter coloTed product when formulated
~or use on crops.
C8~ Elimination of acid resistant pressure release
valves and refluxing equipment.
_
The improved results attainable by the process of
this invention are attributable to the use of limited
proportions of water, which appears to catalYze the
reaction, in conjuction with increased HCl pressures, which
are substantially maintained by avoiding venting of the
reactor during the reaction and detrimental effects
associated with sharp pressure drops in the system.
For simplification of the description, the
following discussion is drawn to the reaction of HCl with
BIC~P, although it is to be understood that mixtures of
BICEP and MEP~A, or MEPHA alone, and/or ~F, ~Br, or HI can
substituted in the following discussion. Similarly, any of
the BICEP or MEPHA derivatives, within the scope of the
above stru~tural formula, can be substituted where
appropriate.
The process of this invention is carried out in a
pressuxe-tight reactor vessel, e.g., an autoclave which is
composed or lined with acid-resistant material and/or lined
with a glass or porcelain or the like, and provided with
means for agitating and for controlling the temperature of
the contents (heating and cooling), for charging BICEP and
water and/or aqueous HCl, and for injecting ~Cl gas,
preferably at the bottom to assist in agitating the
contents. The BICEP and the water and/or aqueous HCl or
aqueous BICEP solution are initially charged, in any order,
to the reactor which is then sealed, the contents heated to
about 110 to 160C., preferably about 1~5 to 145C., and
dry ~Cl gas is injected under pressure to raise the
pressure in the reactor to at least about 100 psig (lbs.
per square inch gauge) up to 500 or more psig, preferably
ii8~
about 150 to 250, more preferably about 165 to 225 psig.
The reaction mixture is then maintained with stirring at
such elevated temperatures with incremental (continuous or
intermittent) addition of sufficient dry HCl gas to
maintain such pressures in the reactor during at least a
major portion, preferably the entire portion, of the
reaction.
For the attainment of the desired improved
results, it is highly important that the amount of water
1~ initially charged to the reactor fall within the range of
about Ool to 1.8 moles, preferably about 0.2 to 1.5 moles,
per mole of the BICEP or related haloalkylphosphonate
charged, and the water concentration is maintained within
this ranqe throuqhout the reaction. The reaction
theoretically requires 2 moles of HCl per mole of BICEP or
related haloalkylphosphonate diester, and 1 mole of HCl
when the monoester is employed as the reactant to produce
the corresponding CEPA or related acid. Although all of
the required HCl could be supplied by the dry ~Cl gas
injected during the reaction, it is most convenient, to
hasten initiation of the reaction and the like, to charge
the above-described controlled proportions of water, in
accordance with this invention, in the form of aqueous HCl,
preferably in concentrated form of at least about 23%, more
preferably at least about 35%, and most conveniently about
37%, by weight. Illustratively, addition of sufficient 37~
aqueous HCl to provide an initial BICEP reaction mixture
containing about 0.6 to 10% water (and 0~4 - 6% HCl)
supplies the 0.1 to 1.8 moles of water per mole of BICEP in
the mixture/ as required in accordance with this invention
--7--
and provides a portion of the HCl needed for the reaction.
Subsequently, the pressure in the reactor can be maintained
with dry HCl gas or with dry HCl gas together with a small
amount of concentrated aqueous acid, e.g., of 37 weight
percent or more acid concentration, provided the 1.8 moles
of water is not exceeded.
The addition of the dry pressurized HCl gas during
the reaction can be controlled manually or automatically.
For example, the addition may be triggered to inject the
1~ gas when the pressure falls to a predetermined lower value
within the required range and the injection stopped when
the pressure has risen to a predetermined upper value
within the required range. Cessation of the reaction is
indicated by failure of the pressure to drop to or towards
said lower value. Alternatively, the addition may be
controlled to inject the gas continuously at a rate
approximating its rate of reaction at the predetermined
pressure in the reactor. Cessation of the reaction is
indicated in this system by a rise in the pressure as the
injected gas remains unreacted and builds up in the
reactor. Operation of the reaction within the above-
described ranges of HCl gas ~ressure automatically and
inherently maintains the concentration of water in the
reaction medium at the above-described concentrations.
The reaction is generally completed in as little
as about 6.5 hours. Lowering the reaction time much below
6 hours has a diminishing effect on cost reduction because
of fixed, rather long heat-up and cool-down cycles. Upon
completion of the reaction, the liquid reaction medium
containing mostly CEPA and ethylene dichloride is cooled to
B~
obtain a two-phase system consisting of an organic phase
containing the ethylene dichloride and an aqueous phase
containing the desired CEPA. The two phases or layers are
separated, as by drawing off or siphoningJ and the aqueous
. phase stripped of water and HCl as by flash evaporation
under reduced pressure to obtain the CEPA in good yield and
in a substantially pure state.
In cases where MEPHA replaces BICEP, in whole or ::
in part, as a starting material in the reaction J temperature ~
and pressure conditions within the upper portion of the above ~ ;
ranges can be employed.
In carrying out the present process, the BICEP
reactant may be essentially pure or in crude form of from
about 75-95% concentration in admixture with undistillable
substances as produced in known manner by isomerization of
tris-~2-chloroethyl) phosphite in the presence of an inert
organic diluent such as cumene, xylene, o-dichlorobenzene,
etc. at elevated tempe~atures such as about 160C.
As indicated above, although the process of this
invention has been described with respect to the conversion
of BICEP to CEPA, the invention is operative with and
inclusive of the use of related homologs and analogs of ~-
BICEP or MEPHA to produce other haloalkylphosphonic acids
.. ,. . ~. .
such as for example the bromo, iodo and fluoroanalogs of
CEPA, and corresponcling halopropylphosphonic,
haloisopropylphosphonic, halohexylphosphonic acids and the
like, preferably having halogen bonded to the terminal
carbon atom of an ethyl group. Instead of BICEP or MEPHA,
there may be employed the corresponding esters of
haloalkylphosphonic acids such as the halogenated bis or
mono -methyl, -propyl, -hexyl esters and the like~ For
agricultural or other uses which may require liberation of
alkene from instant acid products, the halogen is
preferably bonded to the B-carbon atoms. Still other uses
may call for halo-substitution in other positions of the
alkyl group.
The present invention enables the production of
better yields of purer CEPA containing lower amounts of
impurities such as ~EPHA, MEPHA~ and/or bis-(2-chloroethyl)
vinyl phosphonate, and/or lower amounts of water which must
be stripped in relatively shorter reaction times and/or
higher output from the available reactor equipment.
29 The following examples are only iliustrative of
this invention and are not to be regarded as limitative.
All amounts and proportions referred to herein and in the
appended claims are by weight unless otherwise indicated.
EXAMPLE I
A one-gallon stirred glass-lined autoclave is
charged with 1212 g. (4.5 moles of bis-(2-chloroethyl)-2-
chloroethylphosphonate (BICEP) and 30 ml. (35.7 g.) of 37~
aqueous HCl. This mixture contains about 1.0~% HCl, 1.8%
water, by weight, 1.25 moles of water and a molar water:
--10--
37~
BICEP ratio of 0.28:1. The autoclave is sealed, heated to
; about 135C. with stirring, pressurized with dry HCl gas
in]ected at the bottom of the autoclave to about 220 psig,
and the injection continued while maintaining the reaction
mixture at 135C. and 220 psig until the reaction is
completed in about 7 hours (at which time the pressure
ceases to fall after injection of HCl gas). The reaction
mixture is then cooled and discharged from the autoclave.
The upper layer containing ethylene dichloride is separated
from the resulting two-phase liquid system and the lower
aqueous phase containing the CEPA is stripped of water and
HCl by flash evaporation to a final drying temperature of
75C/15 mm. The CEPA so obtained is a clear, crystalline
yellow product, weighs 585 g. and analyzes as follows:
CEPA 90.0% MæpHA 1.0%; HEPHA 0.3%; H3PO4 2.5~; water 0.5%.
EXAMPLE II
The procedure of Example I is repeated except that
(1) the initial charge contains 150 ml. (179 g.) o 37~
aqueous HCl to provide an acid concentration of 4.8% ~Cl
and 8.1% water, by weight or 6.27 moles of water to pro-
vide a molar water: BICEP ratio of 1.4:1, and (2) the
reaction mixture is pressurized with dry HCl gas at 185
psig for 7 hours. The results are: CEPA 92.3~; MEPHA 1.1%;
HEPHA 0.5%; H3PO4 1.5%; water 0.7%.
By way of comparison, the following table
summarizes the inferior results involving processes carried
out with higher water; BICEP molar ratios and pressures of
70-90 psig at 120C.
TABLE A - COMPARATIVE
MOLES REACTION
WATER TIME CEPA MEPHA HEPHA
BICEP HRS. ~ % %
12.5 14 87.7 1.8 2.4
9.4 14 86.7 1.6 0.6
3.5 24 87.2 3.0 0.7
Further, when the CEPA obtained in accordance
with the products of TABLE A are employed in a formulation
containing 24.5% CEPA, 32% propylene glycol and 43.5% water
for use on crops, the formulation ranges in color from
yellow to dark amber and from 0-200 ppm. (based on CEPA) of
black material precipitates on standing 24 hours or more.
Similar formulations prepared with the CEPA produced by the
process of this invention are light yellow in color and no
precipitate forms on standing.
COMPARATIVE EXAMPLE - ANHYDROUS
_ . . ._ ~ . .
A one-gallon stirred glass-lined autoclave is
charged with 1212 g. (4.5 moles) of anhydrous BICEP. The
autoclave is sealed, heated to 150C. and pressurized to
230 psig by injection of dry HCl gas at the bottom of the
autoclave. The reaction mixture is maintained at 150C/230
psig with HCl gas injection until the reaction is complete
in about 10 hours. The reaction mixture is then discharged
and cooled, the CEPA solidifying. The mixture is heated to
75C. and an aliquot of both the ethylene dichloride and
CEPA is removed. The ethylene dichloride is distilled and
the CEPA is dried to a final drying temperature of 75C./15
mm.
-12-
The CEPA so obtained is dark brown and analyzes as
follows: CEPA 93 . 99~; MEPHA 3 .1%; HEPHA O .1~; H3P04 1. 0%;
H20 0 . 4 % .
A formulation containing 24.5~ of this CEPA 32%
propylene glycol and 43.5% water is dark in color and on
~`
standing a precipitate of dark specks and a dark oily layer
. .
are formed~
EXAMPLE III
A one-gallon stirred, glass-lined autoclave is
charged with 931.5 g. (4.5 moles) of mono-2-
chloroethylphosphonate (MEPHA) and 150 ml. (179 g.) of 37~
aqueous HCl. This mi~ture contains about 5.96 weight% HCl
and lQ.2 weight perrent H20 to provide a molar water MEPHA
ratio of about 1.4:1.
The autoclave is then sealed, heated to about
145C. and continuously stirred. Over a period of about
7.5 hours, the system is pressurized three times to 250
psig by injection of dry HCl gas through an acid inlet
valve positioned in the bottom of the reactor. After about
7.75 hours, the reaction is complete and the reaction
mixture is cooled and discharged from the autoclave.
Two liquid phases are formed and the upper liquid
layer containing ethylene dichloride is decanted from the
lower aqueous layer containing CEPA and waterO The lower
aqueous layer is then stripped of water and HCl by flash
evaporation to a final drying temperature of 75.5C./15 mm.
7~
The CEPA product is a substantially colorless,
clear crystalline material weighing about 580 g. and having
the following analysis: CEPA 95.0%; MEPHA 1.5%; HEPHA
0.3%; H3PO4 2~5% and water 0.5%.
EXAMPLE IV
The above reaction of Example II is repeated
except that an equivalent amount of mono-2-fluoroethyl-2-
fluoroethylphosphonate is substituted for MEPHA and an
equivalent amount of HF is substituted for HCl.
Accordingly, the product obtained is 2-
1uoroethylphosphonic acid in good yield and in a high
state of purity.
The same results and good yield of the
corresponding acid product are achieved when mono-2-
bromoethyl-2-bromo-ethylphosphonate or mono-2-iodoe~hyl-2-
iodoethylphosphonate is substituted for MEPHA and the
corresponding hydrogen halide, e.g., HBr or HI, is
substituted for HCl or HF in Examples III or IV; or when
bis(2-fluoroethyl)-2-fluoroethylphosphonate, bis~2-
iodoethyl)-2-iodoethylphosphonate or bis(2-bromoethyl)-2-
bromoethylphosphonate is substituted for BICEP and the
corresponding hydrogen halide, e.g., HF, HI or HBr is
substituted for HCl in Example I.
This invention has been disclosed with respect to
preferred embodiments and it will be understood that
modifications and variations and the substitutions
discussed in the foregoing specification will become
obvious to those skilled in the art and are to be included
within the spirit and purview of this application and the
scope of the appended claims.
-14-
