Note: Descriptions are shown in the official language in which they were submitted.
a~1~
- 1 - 23189-5370
A nlmlber of processes for the introduction of bromine into polyols are
already known. Processes in which phosphorus bromides or thionyl bromide are
employed as the brominating agent or which proceed via a ben~enesulphonate as
intermediate are very costly to carry out, require expensive reagents and are,
for these reasons, not used industrially.
Other processes, in which anhydrous hydrogen bromide and organic sol-
vents, such as toluene or perchloro0thylene, are employed, require large exces-
ses of hydrogen bromide and/or the use of high temperatures and/or pressures, in
order to obtain reasonably acceptable yields. These processes also have no
industrial importance.
Mixtures of hydrogen bromide and glacial acetic acid have also been
employed in the past. In these instances, it was found to be necessary to bind
the water of reaction by the addition of acetic anhydride or acetyl bromide.
The disadvantage of this is that after the reaction, all hydroxyl groups which
have not been substituted by bromine are in the form of acetates, and must first
be liberated again in a transesterificatlon reaction.
Processes in which aqueous hydrogen bromide is employed require
aqueous solutions of hydrogen bromide with concentrations of HBr higher than the
~8% strength hydrobromic acid commercially available in order to be able to
achie-ve good results and acceptable reaction times. This means that the hydro-
bromic acid commercially available must first be concentrated by passing through
gaseous HBr for such processes. In spite of this~ high reaction temperatures
and/or working under pressure in an autoclave are still necessary.
The most favourable processes known at present may be regarded as
those in which the polyols are reacted in the presence of large amounts of
glacial acetic acicl with 48 to 66% strength aqueous hydrogen bromide solution at
normal pressure ~see, for example, J. Org. Chem. 30, 19~5 and 3308 (1965)). The
Ge/ksch(Gai) Le A 21 117WCA
q~
disadvantage of th:is is; however, that the bromohydrins obtained are also com-
pletely or partly ace-tylated on the hydroxyl groups s-till present, and -the free
bromohydrins can only be obtained in a subsequent transesterification reaction.
Eor this, a short~chain alcohol, for example methanolJ and an acid cata]yst are
added, and the acetate formed and the excess short-chain alcohol are distilled
o-ff. Subsequently, the crude bromohydrin thus ob-tained must s-till be purified
by recrystallisation.
The expense of this procedure is obvious from German
Offenlegungsschrift 2,440,612. According to Example 1 of this German
Offenlegungsschrift~ 40 mols of HBr in the form of a 62% s-trength aqueous solu-
tion ar0 reacted with 20 mols of pentaerythritol in the presence of 10 mols of
acetic acid at about 120C. During the reaction, the water in-troduced with the
IIBr solution and formed in the bromination reaction distills off togetiler with
some acetic acid. The rest of the acetic acid is bound in the form of acetates
to the brominated pentaerythritol. In order to remove these acetate groups from
the brominated pentaerythritol, after cooling down, 2 1 of methanol and a
catalytic amount of 62% strength HBr solution are added, and -the mixture is then
heated to boiling. A mixture of methanol and methyl acetate is distilled off.
Before the excess methanol is completely removed, the mixture is neutralized
with methanolic ammonia solution. Subsequently, active charcoal is addedJ heat-
ing is repeated, and the mixture is filtered hot through a filter aid. There-
after, the last residues of methanol are removed by evaporation to dryness. The
crude product thus obtained is recrystallized from trichloroethvlene. Thus in
summary, it is clear that the after-treatment of the reaction product involves
more outlay than the actual bromination.
A process for the preparation of bromohydrins by reaction of a polyol
of the formula
_ 3 _ '~
110- Cli2
0-C~12-C-R
~10- Cl-l
R = ~12O~1, C113 ~r C2 5
with aqueous HBr solution in the presence of organic acids, wa-ter being removedby distillation during the reaction, has now been found, which is characterised
in -tha-t a catalytic amount of a low molecular weight organic acid is employed.Suitable polyols for use in the process according -to the invention are
pentaerythritol, trimethylolethane and trimethylolpropane. In these compounds,
depending on the amount of 11Br solution employed, one or more OH groups can be
replaced by bromine and, in this manner, the corresponding mono- or poly-
bromohydrins or mixtures thereof can be obtained. The polyols to be employed
may have been prepared in any desired manner and may be employed in commerciallyavailable purity.
The concentration of the aqueous HBr solution ca11 vary within wide
limits. For economic reasons, the use oE readily available aqueous HBr solu-
-tions is preferred, for example those with contents of HBr in the range from 20to 50% by weight. However, 11Br solutions of lower and higher concentration can
also be employed. In a preferred manner, 40 to 50% by weight aqueous HBr solu-
tions are employed, and particularly preferably the commercially available,
approximately ~% by weight aqueous HBr solution. The necessary reaction times
can vary depending on the concentration of the HBr solution employed.
The amount of HBr solution substantially depends on the number of O11
groups to be reacted. For example, 0.9 to 2.0 mols of 1-1Br can be employed per
mol of OH group to be reacted. In a preferred manner) l.0 to 1.25 mols of HBr
are employed per mol o-f OH group to be reacted.
Examples of suitable reaction temperatures are -those in the range from
- ~ -
20 to 16n C. In a preferred manner, the process is carried out at 80 to 150 C.
It is also possible to proceed in such a manner that the reac-tion starts at
relatively low temperatures, for example at room temperature, and then increases
to hig}ler temperatures, for example ~0 to l50C.
Tlle pressure is selected so that water formed during the reaction and
other water p-resent, particularly tha-t introduced with the ilBr solution~ dis-
tills off. During this, the organic acid employed and excess ilBr, if present,
may wholly or partly, particularly towards the end of the reaction, also be car-
ried over. In a preferred manner, this removal by distillation is carried out
over a column. Depending on the reaction temperature used, the pressures can be
in the range from, for example, 0.2 to 2 bar, preferably in the range 0.3 to 1.5
bar. The process is particularly preferclbly carried out at normal pressure and
the water is distilled over at about 100 C, bottom temperatures in the range
from about 110 to 130 C then arising.
I-t is an important charact0ristic of the process according to the
invention that, in contrast -to processes hitherto known, it is not carried out
in an acetic acid medium, but only using a catalytic amount of a low molecular
weight organic acid. Examples of suitable low molecular weight organic acids
are carboxylic acids with 1 to 4 C atoms e.g. C3 and C~ carboxylic acids, in
which the alkyl hydrogen atoms can also be partly or totally replaced by halogen
atoms. Examples which may be mentioned are: formic acid, acetic acid, pro-
pionic acid, n-butyric acid, i-butyric acid, monochloroacetic acid, dichloro-
acetic acid, trichloroacetic acid, monochloropropionic acid, dichloropropionic
acid, monofluoroacetic acid, difluoroacetic acid and trifluoroacetic acid.
Acetic acid is preferably employed.
The amount of low molecular weight organic acid employed can, for
example, be 0.1 to 3% by weight relative to the total weight of the reaction
batch. This amount is preferably 0.1 to 2% by weight.
- 5 ~
The reac-tion time :Eor the reaction according to the inven-tion is
generally between 5 and 20 hours. The reaction time particularly depends on -the
amoun-t of low molecular weight organic acid employed, on the nature of the low
molecular weight organic acid, on the concentration o-E the aqueous ilBr solution
and on -the rate at which the water is distilled off.
~ he process according to the invention can be carried out discontinu-
ously o:r continuously. A reaction cascade is suitable, :Eor example, for carry-
ing it out continuously.
In a preferred embodiment oE the process according -to the invention,
pentaerythritol, trimethylolethane or trimethylolpropane is reacted, after the
addition of 0.1 to 2% by weight of acetic acid, relative to the total weight of
the reaction batch, with commercially available approximately ~8% strengtll
aqueolls ilBr solution in a reaction vessel which is prov:ided with a packed column
with reflux divider. 1.0 to 1.25 mols of HBr are employed per mol of OH groups
to be reacted. The contents of the reaction vessel are heated at normal pres-
sure to about 120 to 130C, and -the heat supply and reflux ratio are controlled
in such a manner that, at the top of the column, initially at 100C, only water
can be taken o:Ef. Towards the end of the reaction, the take-off temperature is
allowed to rise to about 120C. Obviously it is also possible to work under
~0 reduced pressure and with correspondingly lower distillation temperatures. In
this way, up to 90% o-E the acetic acid employed and residues of unreacted HBr
are carried over in addition to water.
Bromohydrins are obtained in the process according to ~he invention in
yields of about 85 to 90% of theory. The product obtained generally contains
small amounts of by-products, principally bromohydrins having either one atom of
bromine more or one atom less. Frequently, it can be used immediately as it is
obtained. If purer products are desired, purification can be carried out, for
- 6 -
example, by distillation in vacuo; this however does not generally succeed in
completely removing by-products Bromohydrins of high puri~y ~more than 99%
pure) can be obtained i~y recrystallization for example -Erom trichloroethylene or
chlorofo-rm.
The process according to the invention offers, in particular, the
Eollowing advantages compared to -the processes of the sta-te of the art: the
bromohydrins are produced in such purity that there is no need for further puri-
fication a:Eter removal from the reaction mixture by distillation. The trarls-
esterification reaction with an alcohol which was hitherto necessary, and
followed the actual reaction is omitted and this saves one reaction step.
Furthermore7 only a very small amount of organic acid is required.
It must be regarded as exceptionally surprising that, according to the
invention, it is possible to obtain such goocl results with only very small
amounts of organic acids, since substantially larger amo~m-ts of acetic acid had
hitherto been considered necessary.
The bromohydrins which may be prepared according -to the invention are
known products, which can be used in a known manner for the flameproofing of
plas-tics ~see, for example, European Published Specification 0,018,176)~
In addition, the bromohydrins prepared according to the invention may
be readily modified. In this way, for example, they find many uses in the form
of their carboxylation products, carboxylates, phosphates and carbonates as
flameproofing agents ~see, for example, German Published Offenleg-ungsschriften
2,157,214 and 2,701,856).
The following examples illustrate the process according to the inven-
tion without restricting it in any way.
_ 7 _
~xamplas
ExamE~le 1
Prepara-tion of 2,2-bis~bromomethyl)propan-1,3-diol
2,720 g (20 mols) of pentaerythritol, 6,800 g of ~8% strength aqueous
IIBr solution (40.3 mols) and 150 g of acetic acid were initially introduced into
a 10 1 round-bottomed flask, which was provided with a heating mantle, stirrer
and a 50 cm-long packed column with a reflux divider. ~fter the temperature at
the top of the column had reached 100 to 102C at normal pressure, the water
was distilled off at this temperature. The bottom temperature was 125 to 130 C
during this. A:Eter 6 hours, the major part of the water had been taken off.
While the bottom temperature slowly rose to 150C, the reflux ratio was adjustedto 2:1 (2 parts take-off, 1 part reflux). In this way, the last residues of
water were distilled off in the next 3 hours. More volatile by-products were
then distilled off under water-pump vacuum at 10 mbar together with the last
residues of water. :[n this way, 4,460 g of distillate were obtained, which con-tained 100% of the calculated amount of water, 79% of the acetic acid employed
and 1.5% of the IIBr employed. In addition, in the distillate there was still
about 35 g of volatile organic compounds which were not identified.
The residue was distilled at 120 to 130C in vacuo at 0.2 mbar. In
this way, 4,575 g, corresponding to 87% of theory, of a transparent product wereobtained, which immediately crystallized. The product thus obtained had the
following composition (determined by HPLC = high pressure liquid chromatography):
2.4% by weight of 2-bromomethyl-2-hydroxymethylpropan-1,3-diol
84.2% by weight of 2,2-bis(bromomethyl)propan-1,3-diol
12.1% by weight of 2,2,2-tris(bromomethyl)ethanol
Llle product thus obtained could be used without :turther purification.
-- 8 --
E~am~le 2
Comparison example according -to German Offenleg~mgsschrift 2,~40,612, but with
~8% strength aqueous HBr solution
20 mols of hydrogen bromide in the :Eorm of a ~8% strength aqueous solu-
tion were mixed with 10 mols of pentaerythritol and 5 mols of glacial acetic
acicl and heated to reflux in an apparatus analogous to that in Example 1. The
water which had been introduced and that which was produced was taken off at
normal pressure at a bottom temperature of 120 to 150 C and a top temperature of101 to 102C in the course of 7 hours. In order to liberate -the brominated
pentaerythritol which was present in the form of the acetate, transesterifica-
tion with methanol was carried out. For this, after cooling, 1 1 of methanol
and 2 ml of ~8% strength HBr solution were adcled~ and the batch was heated to
reflux. Then a mixture of methanol and methyl acetate was distilled ofE.
A:Eter 2 hours, the temperature at the top of the column had reached the boilingpoint of methanol. The residue was then cooled down, neu-trali~ed with ~ N
methanolic ammonia solution and 80 g of active charcoal was added. The mixture
was heated a further ~5 minutes under reflux and thereafter filtered hot througha filter aid (Microfil)*. The pale yellowish filtrate was then evaporated to
dryness. In this way, 2,160 g (82%) of a crude product were ob-tained with the
following composition (determined by HPLC):
1% by weight of 2-bromomethyl-2-hydroxymethylpropan-1,3-diol
78% by weight of 2,2-bis(bromomethyl)propan-1,3-diol
20% by weight of 2,2,2-tris(bromomethyl)ethanol.
Exam~
___
Preparation of 2,2-bis(bromomethyl)propan-1,3-diol with propionic acid as the
catalyst
10 mols of pentaerythritol and 20 mols of HBr in the form of an
* Irade Mark
aqueous ~8% strength solution using 2% by weight of propionic acid were reacted
in a manner corresponding to that described in Example 1. The total water which
had been introduced and which was -formed was distilled off at a top temperature
of 100 -to 102 C and a bottom temperature of 120 to 140 C in the course of 7
hours. After distillation of the residue in vacuo, 2,332 g (89% of theory) of a
product with the Eollowing composition were obtained ~determined by IIPLC):
1.7% by weight of 2-bromomethyl-2-hydroxymethylpropan-1,3-diol
83.5% by weight of 2,2-bis(bromomethyl)propan-1,3-diol
13.8% by weight of 2,2,2-tris~bromomethyl)ethanol.
xample 4
Preparation of 2,2-bis(bromomethyl)propan-1,3-diol using 24% by weight HBr solu-
tion
,
680 g of pentaerythritol, 3,400 g of 24% strength aqueous hydrobT~omic
acid and 40 g of acetic acid were reacted in the manner described in Example 1.
Af-ter 5 hours reaction time, 2,350 g of water had distilled over. Af-ter the
addition oE a further 12 g of acetic acid, the residual water was distilled off
in the course of 2 hours. A:Eter distillation of the residue in vacuo, 82% of a
product of the :Eollowing composition was obtained (determined by HPLC):
7.9% by weight oE 2-bromomethyl-2-hyclroxymethylpropan-1,3-diol
84.2% by weight of 2,2-bis(bromomethyl)propan-1,3-diol
5.6% by weight of 2,2,2-tris(bromomethyl)ethanol.
Example 5
Preparation of 2-bromomethyl-2-hydroxymethylbutan-l-ol
268 g ~2 mols) of trimethylolpropane were dissolved in 374 g (corres-
ponding to 2.2 mols) of 48% strength aqueous hydrobromic acid and 6 g of acetic
acid in a 1 l three-neck flask and stirred for about 3 hours at room temperature.
Thereaf~er, tile solution was heated to boiling at 400 mbar and water distilled
- 10 -
off over a packed column with a reflux divider up to a bo-ttom temperature of
130C in the course of 5 hours. The residual hydrobromic acid was taken off at
20 mbar~ 394 g of residue remained which contained 80% of 2-bromomethyl-2-
hydroxymethylbutan-l-ol by gas chromatographic analysis. 270 g (68% of theory)
of the pure compound were obtained by recrystallization from toluene and water.
_xam~e 6
Preparac.ion of 2,2-bis~bromomethyl)butan-1-ol
2,680 g (20 mols) of trimethylolpropane, 8,500 g (50 mols) of 48%
strength aqueous hydrobromic acid and 300 g of acetic acid were mixed in a lO 1
three-neck flask and stirred a* room temperature overnight. Then at 400 mbar,
3 1 of distillate were taken off over a packed column at a reflux ratio of 2:1
in the course of 8 hours. After the major part of the hydrobromic acid had
reacted, water was further distilled off at a pressure of l bar up to a bottom
temperature of 150C. Portions of product which were also carried over in the
distillate and separated out in the collector, were combined with the bottom
product beEore the subsequent distillation. Thereafter, the residue was dis-
-tilled at 135 to l40C in vacuo at 16 mbar. 4,559 g of an oil which slowly cry-
stallized were obtained, which contained 90% of 2,2-bis(bromomethyl)butan-1-ol
by gas chromatographic analysis.
0 Example _
aration of 2-bromomethyl-2-methylpropan-1,3-diol
480 g (4 mols) of trimethylolethane, 748 g (4.4 mols) of 48% strength
aqueous HBr solution and 12 g of acetic acid (1%) were initially introduced into
a 2 1 capacity apparatus analogous to that in Example 1. This mixture was
stirred at room temperature for 3 hours and then water was taken off at 300 mbar
up to a bottom temperature of 130 C. The temperature at the top of the column
was about 80C clu:ring this. After 9 hours, all the water had passed
over. The remaining product was distilled at 0.7 mbar
and a boiling point of 120 to 130C. ~60 g (90%) of 2-
bromomet~lyl-2-methylpropan-1,3-diol were obtained, which
contained 10% of the corresponding dibrominated compound
and about 4% of starting material.
Example 8
Preparation of 2,2,2-tris(bromomethyl)ethanol
_ . . _~_
10 mols (1,360 g) of pentaery-thritol, 37.5 mols of
HBr in the form of the aqueous 48% strength solution and
100 g of acetic acid were initially introduced into an
apparatus analogous to Example 1. After heating to
reflux for 3 hours, water which had been produced and that
which had been introduced could be distilled off ata top tem-
perature of 100C to 102C. The total amount of water
and the excess hydrogen bromide distilled off in the course of the
next 9 hours. In this way, 3,985 g of distillate were
obtained. The bottom temperature rose from 120C to
145C in this period. After distillation in vacuo at
110C to 120C and 0.5 mbar, 2,95g g (91%) of 2,2,2-tris-
(bromomethyl)ethanol were obtained of the following com-
position (according to HPLC):
1.5% by weight of 2-bromomethyl-2-hydroxymethylpropan-
1,3-diol
9.3% by weight of 2,2-bis(bromomethyl)propan-1,3-diol
88 % by weight of 2,2,2-tris(bromomethyl)ethanol.
Le A 21 117
