Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~)41~40
E~CKGROUND OF THE INVENTION
This invention relates to the production of alpha-
resorcylic acid and more particularly to the hydrolysis of 3,5-
diamino benzoic acid with ammonium bisulfate to produce alpha--
re`sorcylic acid.
Alpha-resorcylic acid (3,5-dihydroxy benzoic acid) ~ -
is generally in the form of white crystals with a melting point
of 237C. Alpha-resorcylic acid is used as an intermediate for
dyes, in pharmaceuticals, as a light stabilizer and in resins.
It is used, for example, as an ultraviolet absorber in the formu-
lation of suntan lotions. -
SUMMARY OF THE INVENTION
In accordance with this invention, alpha-resorcylic
acid is made by the ammonium bisulfate hydrolysis of 3,5-diamino
benzoic acid by contacting the 3,5-diamino benzoic acid with
at least 4 but preferably 6 moles of ammonium bisulfate per
mole of the 3,5-diamino benzoic acid in aqueous solution at a
temperature of about 200-300C, but preferably 220 C, for a time
sufficient to hydrolyze the 3,5-diamino benzoic acid to alpha-
resorcylic acid. The reaction may be expressed as
COOH COOH
~ NE14HS04 > O +(NH4)zSO4
NH2 ~ NH2 H2o OH H
.
The aqueous solution is then cooled and the product alpha-resor-
cylic acid extracted using a suitable inert solvent. Ilydrolysis
may be repeated by reheating the reaction mixture after extrac-
tion and the ammonium sulfate can be regenerated for reuse in
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1~)41~40
the reaction by evaporatlng the water and heating the melt of the
mixed ammonium sulfates at a temperature of 310-450 C. Upon
cooling the resulting ammonium bisulfate is dissolved in water,
adjusted to the desired concentration and recycled to the reaction
zone. The solvent solution from the extraction step is evapor-
ated to give the alpha-resorcylic acid in substantially pure form.
DETAILED DESCRIPTION
In accordance with this invention, 3,5-diamino
benzoic acid is hydrolyzed in an aqueous medium through the use
of ammonium bisulfate to produce alpha-resorcylic acid. The
by-product salt can be regenerated to ammonium bisulfate for
reuse in the process.
The composition of the hydrolysis medium is of par-
ticular importance. A minimum of 4 but preferably 6 moles of
ammonium bisulfate, based on the number of moles of 3,5-diamino
benzoic acid, is necessary in order to provide a reasonable
yield of alpha-resorcylic acid in a single hydrolysis reaction.
The hydrolysis can be carried out in one step or it can be con-
tinued sequentially by terminating the reaction, cooling, ex-
tracting the product and reheating the hydrolysis mixturewithout further addition of reactants. A one-step hydrolysis
is desirable from the standpoint of ease and efficiency of
operation, although an increase in yield can be achieved by a
second hydrolysis of the reaction mixture after removing the
product from the first hydrolysis. From the standpoint of ob-
taining high yields in a single hydrolysis step, the use of
high concentrations of ammonium bisulfate up to the point of
saturation of the aqueous solution is desirable. With high
concentrations, a practical problem arisès in the handling of
large quantities of salt.
Water must be present in an amount sufficient to
provide for hydrolysis and also to serve as a diluent or solvent
for the 3,5-diamino benzoic acid, ammonium bisulfate and the
ammonium sulfate formed during the course of the reaction. At
least 40 but preferably 60 moles of water per mole of 3,5-
diamino benzoic acid must be present to dissolve sufficient
quantities of ammonium bisulfate. As the amount of ammonium
bisulfate is increased, more water, up to about 120 moles, is
required. The use of excess water results in a practical pro-
blem of water removal during the ammonium bisulfate regeneration
- step.
The reaction temperature can vary over a wide range
between about 200 to 300C. At temperatures below about 200C.
an unduly long reaction time is required and the yields are
generally low. As the temperature is increased the pressure
must be correspondingly increased to maintain the reaction
solution in the aqueous phase. At temperatures as high as 300C.,
a steam pressure of up to about 1500 psig is required for this
purpose and there is some danger of resin formation if the
contact time is too long. No advantage is obtained by increasing
or decreasing the pressure to a value other than that sufficient
to provide for a liquid reaction medium. To avoid the use of
considerable pressure, with the corresponding equ.pment
requirements, temperatures in the range of 220-260C. are
- preferred.
The reaction time or contact time varies primarily
with the temperature and to a lesser extent with the mole ratio
- of the reactants. At a minimum temperature, e.g., 200C., a
per pass reaction time of 8 hours is ordinarily required. At
220C. effective results from the standpoint of yield are
- obtained using a two pass hydrolysis reaction and a reaction time
. 3
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1~)41540
of 6 to 7 hours per pass. Alse at 220 C. good results are
obtained in a single pass hydrolysis step if the reaction time
is extended to about 13 hours. At temperatures about 250C.,
hydrolysis can occur in five minutes to a half hour. From a
practical standpoint an overall per pass hydrolysis time can
be considered to be from 5 minutes to 13 hours.
Hydrolysis is carried out in a zone which is resis-
tant to any substantial attack by the ammonium bisulfate or the
3,5-diamino benzoic acid. At very low temperatures within
the useful range, an ordinary galss lined Pfaudler kettle can
be used. ~hen higher temperatures are required, other construc-
tion materials become necessary. At temperatures up to 220-
230C. Teflon lined reactors are effective. Higher temperature
ranges require the use of more durable equipment such as tanta-
lum lined reactors.
After the period of hydrolysis, the reaction mix-
ture is cooled to prevent resinification of the product in the
acidic aqueous reaction mixture and to enable the separation of
the by-product by organic solvent extraction. Any substantially
~0 water-immiscible solvent which will dissolve the alpha-resorcylic
acid is useful. Ethyl ether is the preferred solvent. The
~organic solvent phase is then separated from the reaction
mixture by decantation and the alpha-resorcylic acid is removed
from the solvent by evaporation of the solvent.
After removal of the alpha-resorcylic acid, the
resulting aqueous reaction mixture can be reheated to the
hydrolysis temperature for a second or even a third hydrolysis
step. The second and subsequent hydrolysis steps are carried
out as before by heating the reaction mixture to the appropriate
temperature of hydrolysis for the desired period of time,
cooling and removing the alpha-resorcylic acid product by solvent
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extraction. 1~41~40
Ammonium sulfate by-product is regenerated to ammo-
nium bisulfate for reuse in the process by removing the residual
water from the remaining reaction mixtùre and heating the molten
salt, primarily mixed ammonium sulfate, and ammonium bisulfate
at atmospheric pressure at a temperature between 310-450C At
temperatures below 310C., an unduly long time is required to
effect decomposition. No practical advantages are seen in
using temperatures higher than 450C. and above this temperature
the bisulfate tends to decompose. At 330C., 75-95 percent of
the ammonium sulfate is converted in a few minutes to ammonium
bisulfate. Slightly higher conversions are obtained at higher
temperatures although this advantage is offset by the increased
equipment cost required. During the decomposition of the ammo- -~
nium sulfate, residual organic materials may be pyrolyzed to
black granules resembling activated charcoal. This charcoal-
like material is easily removed by dissolving the mixture of
ammonium sulfate and ammonium bisulfate product in water
foll~ræ by a filtration step. The ammonia formed during the
decomposition can be recovered and used in other chemical
processes. The clear, filtered salt solution, the salt portion
of which is 75-95 pe~cent ammonium bisulfate, is adjusted to the
desired concentration and is recycled to the reaction mixture
for hydrolysis of additional 3,5-diamino benzoic acid.
The invention is further illustrated by the
following example of a preferred embodiment.
A solution of 3,5-diamino benzoic acid (33 g.,
0.18 moles) of 90~ purity, ammonium bisulfate (138g., 1.2 moles)
and water (216g., 12 moles) was heated to 220C. for 6-7 hours.
The amber colored reaction mixture was cooled, was filtered,
and was shaken with ether (2 x 200 ml) for two extractions.
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The aqueous solution after boiling to remove dissolved ether was
heated again for 6-7 more hours at 220C. for another hydrolysis.
The reaction mixture was cooled and was extracted twice with
ethyl ether (2 x 250 ml).
The ether extraction solutions were stripped to
dryness on a steam bath and the white, crystalline, substantially
pure alpha-resorcylic acid remained. The first ether extract
gave 8 g. and the second ether extract gave 9 g. of alpha-
resorcylic acld for a total yield of 61%.
The aqueous reaction medium remaining after the
ether extractions was decomposed to provide bisulfate for re-
cycling as the hydrolyzing agent. To this end, the aqueous
medium is heated and the inorganic sulfates present after
evaporating the medium to a dry salt weighed 144g. An aliquot
of the salt was titrated with 1/10 N NaOlI in the presence of
brom cresol blue indicator and was found to be 87% bisulfate
(13% ammonium sulfate by difference). This mixed, dry salt
was heated in an oil bath and could be stirred easily after
- reaching 146C. which is the melting point of ammonium bisul-
fate. At 298C. for 2 min., the salt weighed 142.4 g. and was
70% ammonium bisulfate by titration. Heating was continued
until a temperature of 312C. wa~ reached and the melt was
held at 312C. for 12 minutes, at which time the ammonium
bisulfate content was 95%; the salt weighed 141g. (theoretical
weight loss). The loss in weight of the salt on heating was
due to ammonia evolution. The organic material in the medium
was converted to fine carbonaceous particles during the heating
of the melt. The thermally treated salt mixture was taken up in
water and the black mixture filtered. After filtering, the
ammonium bisulfate solution was clear. Evaporation of the
filtrate gave light yellow ammonium bisulfate crystals. These
- crystals can be used for further hydrolyzing of 3,5-diamino
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benzoic acid. 1'~41S4~
The foregoing has presented a simple and effective
process for the production of alpha-resorcylic acid.
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