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Патент USA US2113248

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2,113,248
Patented Apr. 5, 1938
UNlTED STATES
PATENT OFFICE
2,113,248
PURIFYING BORIC ACID
Frantz F. Berg, Floral Park, N. Y., assignor to
E. R. Squibb & Sons, New York, N. Y., a cor
poration of New York
No Drawing. Application November 2'7, 1937,
Serial No. 176,891
10 Claims.
This invention relates to the puri?cation of
commercial-grade (“technical”) boric acid.
Commercial-grade boric acid usually contains
an impurity (or impurities) causing aqueous and
5 alcoholic solutions thereof to appear hazy, a fact
which considerably impairs the usefulness and
acceptability of the boric acid, especially for
pharmaceutical purposes. An analysis of such
boric acid generally indicates the presence of
minute quantities of arsenic, heavy metals, chlo
rides, sulfates, and borax (the last being of the
order of 02% or less). Heretofore, the elimina
tion of such impurities Was e?ected only with
considerable difficulty, ordinary recrystallization
15 and/or repeated precipitation of the boric acid
20
strong inorganic acid, and recovering the boric
acid from the solution.
4. The process of purifying commercial-grade
boric acid which comprises treating a hot aqueous
acid from the solution.
mercial-grade boric acid.
It has been found that the haze-causing im
proportion (e. g. about 0.05%) of a strong inorganic acid (e. g. hydrochloric or sulfuric acid).
More speci?cally, the commercial-grade boric acid
is dissolved in water to form a hot concentrated
solution, which is ?ltered, treated with a small
quantity of a strong inorganic acid (preferably
concentrated sulfuric acid), and cooled; the boric
acid is deposited out as a crystalline product,
which yields crystal-clear aqueous and alcoholic
solutions. Preferably, the mother liquor remain
ing after separating the precipitated boric acid is
15
strong inorganic acid, and recovering the boric
5. The process of purifying commercial-grade
boric acid which comprises treating a hot con 20
centrated aqueous solution thereof with a small
proportion of a strong inorganic acid, and re
covering the boric acid from the solution.
6. The process of purifying commercial-grade
boric acid which comprises treating a hot con
centrated aqueous solution thereof with a small 25
proportion of concentrated sulfuric acid, cooling,
and separating the precipitated boric acid.
7. The process of purifying commercial-grade
boric acid which comprises preparing a hot con
30
centrated aqueous solution thereof, adjusting the
pH of the solution to 3.0-4.0 by adding a strong,
returned to the cycle of operations, 1. e. is used
inorganic acid, and recovering the boric acid from
the solution.
8. The process of purifying commercial-grade
as the aqueous solvent for the puri?cation of a
boric acid which comprises preparing a hot con
succeeding batch of commercial-grade boric acid.
The following example is illustrative of the
invention: 300 pounds of commercial-grade boric
centrated aqueous solution thereof, adjusting the
pH of the solution to 3.0-4.0 by adding concen
trated sulfuric acid, and recovering the boric acid
from the solution.
9. The process of purifying commercial-grade
boric acid which comprises preparing a hot con
centrated aqueous solution thereof, adjusting the
pH of the solution to 3.0-4.0 by adding concen
trated sulfuric acid, cooling to about 30° C‘. or less 45
and separating the precipitated boric acid.
10. The cyclic process of purifying commercial
grade boric acid which comprises preparing a
hot concentrated aqueous solution thereof, ad-l
justing the pH of the solution to 3.0-4.0 by adding 50
4 O acid is dissolved in 150 gallons of hot water; the
solution is heated to about 93° C., and the speci?c
gravity adjusted to about 1.04 by adding the
requisite amount of commercial-grade boric acid;
the solution is then ?ltered, and concentrated sul
furic
acid is added to the ?ltrate until the pH
45
thereof is 3.0 to 4.0; the solution is cooled to about
30° C. or lower, whereupon the boric acid sep
arates in crystalline form; the crystals are sep
arated from the mother liquor by centrifugation,
50 and washed with cold distilled water. The boric
acid thus obtained is exceptionally pure, forming
crystal-clear aqueous and alcoholic solutions.
55
taining a small proportion of concentrated sul
furic acid.
3. The process of purifying commercial-grade
boric acid which comprises treating an aqueous 10
solution thereof With a small proportion of a
It is the object of this invention to» provide a
simple and economical process for purifying com
eliminated by recrystallizing the boric acid from
35
boric acid which comprises recrystallizing the
boric acid from an aqueous solution thereof con
solution thereof with a small proportion of a
an aqueous solution thereof containing a small
3O
boric acid from an aqueous solution thereof con
taining a small proportion of a strong inorganic
acid.
2. The process of purifying commercial-grade
being ineffective.
purities in commercial-grade boric acid can be
25
(Cl. 23-149)
a strong inorganic acid, cooling, separating the
precipitated boric acid, and using the mother liq~
The invention may be variously otherwise em
uor for the preparation of a solution of a sub
bodied, within the scope of the appended claims.
sequent batch of commercial-grade boric acid
to be puri?ed.
I claim:
1. The process of purifying commercial-grade
boric acid which comprises recrystallizing the
FRANTZ F. BERG.
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