Process for production of alkenediols

Alkenediols are produced by hydrolysis of a dibromoalkenes in the presence of alkali metal formate. In a preferred embodiment, alkenediols, and particularly 2-butene-1,4-diol, are produced in a series of steps comprising bromination of conjugated diene with cupric bromide, hydrolysis of the resulting dibromobutenes to alkenediols in the presence of alkali metal formate, and regeneration of cupric bromide and alkali metal formate such that only conjugated diene, oxygen and water are consumed.

BACKGROUND OF THE INVENTION 
This invention relates to the production of alkenediols. In a specific 
aspect, the invention relates to the production of alkenediols, and 
particularly 2-butene-1,4-diol, according to a series of reactions in 
which only conjugated diene, water and oxygen are consumed. 
2-butene-1,4-diol is well known as a solvent in various chemical processes 
and as a starting material for the production of 2,5-dihydrofuran, another 
useful solvent. Further, 2-butene-1,4-diol can be hydrogenated to 
1,4-butanediol which is used in the production of tetrahydrofuran, certain 
polyesters and polyurethanes. 
In the past, a number of methods have been proposed for the production of 
2-butene-1,4-diol and other alkenediols. One such method, disclosed in 
Sakomura et al., U.S. Pat. No. 3,911,032 (Oct. 7, 1975), involves 
hydrolysis of 1,4-dichloro-2-butene in an aqueous solution of alkali metal 
formate. According to this proposal, conversion of 1,4-dichloro-2-butene 
to 2-butene-1,4-diol is substantially complete. Further, substantially 
complete conversion of mixed dichlorobutene isomers to 2-butene-1,4-diol 
can be accomplished by conducting the hydrolysis reaction in the presence 
of elemental copper, iron, or zinc or a halide, formate, oxide, carbonyl 
or hydroxide thereof. 
Vasey et al., U.S. Pat. No. 4,160,115 (July 3, 1979) discloses preparation 
of 2-butene-1,4-diol by reaction of butadiene with water and oxygen in the 
presence of copper, nickel, cobalt, chromium, manganese, molybdenum or a 
halide or organic acid salt thereof. The reaction is conducted at 
50.degree. to about 150.degree. C., preferably in a water-miscible 
solvent. 
Childs, U.S. Pat. No. 4,164,616 (Aug. 14, 1979) discloses preparation of 
alkanediols and alkenediols by a series of reactions involving 
halogenation of conjugated diene with molecular chlorine, bromine or 
iodine; acetolysis of the result in the presence of a salt of an alkali 
metal or alkaline earth metal, dissolved or dispersed in an organic acid 
solvent, to form diacetoxyalkene; hydrogenation of diacetoxyalkene to the 
corresponding diacetoxyalkane; hydrolysis of diacetoxyalkane to 
1,4-alkanediol, preferably under basic conditions using an alkali or 
alkaline earth hydroxide; and regeneration of starting materials by 
passing an electric current through an aqueous solution of by-product 
metal halide from the acetolysis step to regenerate halogen for use in the 
halogenation step, hydrogen for use in the hydrogenation step and metal 
hydroxide for use in the hydrolysis step. The sequence of the 
hydrogenation and hydrolysis steps may be reversed according to the 
patentee. 
Although alkenediols can be obtained according to the above-described 
processes, various disadvantages are encountered. For example, the 
dichlorobutenes employed as starting materials in the process of Sakomura 
et al. are expensive and the hydrolysis reaction results in formation of 
alkali metal chlorides which must be disposed of. Further, recovery of 
metal formate from the hydrolysis mixture requires neutralization with 
caustic. Accordingly, in the overall reaction scheme of the Sakomura et 
al. process, valuable chlorine and caustic are consumed and less valuable 
metal chlorides are formed. The process of Vasey et al. suffers from low 
yields and conversion rates as shown in the examples. Further, provision 
is not made for regeneration of starting materials. Such problems are 
avoided in the process of Childs; however, that process is relatively 
complex and the use of electricity for regeneration adds cost to the 
process. 
Accordingly, it would be desirable to provide an improved process for 
preparation of alkenediols. It is an object of this invention to provide 
such a process. A further object of the invention is to provide an 
improved process for the preparation of high yields of alkenediols without 
consumption of costly reactants. A further object of the invention is to 
provide for the preparation of alkenediols according to a series of 
reactions wherein only conjugated diene, water and oxygen are consumed. A 
specific object of the invention is to provide an improved process for the 
preparation of 2-butene-1,4-diol wherein only 1,3-butadiene, water and 
oxygen are consumed. Other objects of the invention will be apparent to 
persons of skill in the art from the following description and the 
appended claims. 
It has now been found that the objects of this invention can be attained by 
contacting dibromoalkenes with alkali metal formate under conditions 
effective to hydrolyze the dibromoalkenes to alkenediols. According to a 
preferred embodiment of the invention, dibromoalkenes prepared by 
bromination of conjugated diene with cupric bromide are hydrolyzed in the 
presence of aqueous alkali metal formate, and cuprous bromide, alkali 
metal bromide and formic acid generated in the bromination and hydrolysis 
steps are contacted with molecular oxygen under conditions effective to 
regenerate cupric bromide and sodium formate which can be re-used in 
bromination and hydrolysis. 
Advantageously, preparation of alkenediols according to this invention 
results in high yields of the desired products. Further, according to a 
preferred embodiment of the invention, high yields of alkenediols are 
obtained according to an overall reaction scheme in which only conjugated 
diene, water and oxygen are consumed. The present invention gives 
particularly good results when employed in the production of 
2-butene-1,4-diol from dibromobutenes as hydrolysis of the latter in the 
presence of alkali metal formate results in substantially complete 
hydrolysis of 1,4-dibromo-2-butene isomer to 2-butene-1,4-diol, and in 
addition, isomerization takes place such that at least a portion of any 
3,4-dibromo-1-butene present in the intial charge is converted to 
2-butene-1,4-diol. Accordingly, costly separation operations and the use 
of additional metals or compounds thereof are not required. According to a 
particularly advantageous embodiment of the invention, 2-butene-1,4-diol 
is prepared by a continuous process involving bromination of 1,3-butadiene 
in the presence of cupric bromide, followed by hydrolysis of the resulting 
dibromobutenes in the presence of alkali metal formate to form high yields 
of 2-butene-1,4-diol, with regeneration of cupric bromide and metal 
formate and recycle thereof. The process according to this aspect of the 
invention can be represented as follows: 
EQU H.sub.2 C:CHCH:CH.sub.2 +2CuBr.sub.2 .fwdarw.BrH.sub.2 CCH:CHCH.sub.2 
Br+2CuBr 
EQU BrH.sub.2 CCH:CHCH.sub.2 Br+2H.sub.2 O+2MOOCH.fwdarw.HOH.sub.2 
CCH:CHCH.sub.2 OH+2MBr+2HOOCH 
EQU 2CuBr+2MBr+2HOOCH+1/2O.sub.2 .fwdarw.2CuBr.sub.2 +2MOOCH+H.sub.2 O 
As used above, M represents alkali metal. The net reaction from the above 
is as follows: 
EQU H.sub.2 C:CHCH:CH.sub.2 +H.sub.2 O+1/2O.sub.2 .fwdarw.HOH.sub.2 
CCH:CHCH.sub.2 OH 
DESCRIPTION OF THE INVENTION 
Broadly, the method of this invention comprises contacting dibromoalkene 
with alkali metal formate under hydrolysis conditions to form alkenediol. 
According to a more specific aspect of the invention, the dibromoalkene 
which is hydrolyzed in the presence of alkali metal formate is prepared by 
bromination of conjugated diene with cupric bromide, and the cuprous 
bromide formed as a by-product of the bromination step, as well as alkali 
metal bromide and formic acid by-products of the hydrolysis step are 
contacted with molecular oxygen under conditions effective to regenerate 
cupric bromide and alkali metal formate which can be re-used in 
bromination and hydrolysis. 
In greater detail, alkali metal formates useful according to this invention 
include sodium formate, potassium formate, and other water-soluble alkali 
metal formates. Mixtures also can be used if desired. Sodium formate and 
potassium formate are preferred from the standpoint of cost and 
availability, best results being attained with sodium formate. 
The dibromoalkene starting materials employed according to this invention 
are those containing 4 to about 12 carbon atoms corresponding to the 
formula R.sub.2 BrCCR:CRCBrR.sub.2 or R.sub.2 C:CRCBrRCBrR.sub.2 wherein 
each R is independently hydrogen or an alkyl radical of 1 to about 8 
carbons. Mixtures of dibromoalkenes corresponding to the stated formulae 
and having identical R groups (e.g., a mixture of 1,4-dibromo-2-butene and 
3,4-dibromo-1-butene) also can be used if desired. However, in order to 
maximize alkenediol yields, the dibromoalkene starting material preferably 
comprises a major portion of dibromoalkene of the formula R.sub.2 
BrCCR:CRCBrR.sub.2. More preferably, at least about 75 mole % of the 
initial dibromoalkene charge corresponds to such formula. 
Specific examples of useful dibromoalkenes include 1,4-dibromo-2-butene, 
3,4-dibromo-1-butene, 1,4-dibromo-2-pentene, 3,4-dibromo-1-pentene, 
1,4-dibromo-2-hexene, 2,5-dibromo-3-hexene, 1,4-dibromo-2-methyl-2-hexene, 
2,5-dibromo-3-octene, 4,7-dibromo-5-decene and 1,4-dibromo-2-dodecene. The 
present invention gives best results in production of 2-butene-1,4-diol 
from 1,4-dibromo-2-butene or mixtures thereof with up to about 20 mole % 
3,4-dibromo-1-butene. 
The dibromoalkenes employed as starting materials according to this 
invention can be prepared by any suitable means. Bromination of conjugated 
diene with suitable brominating agents such as molecular bromine or cupric 
bromide is preferred in order to obtain dibromoalkenes containing 
desirably high levels of the preferred dibromoalkene identified 
hereinabove. As discussed in greater detail hereinbelow, the 
dibromoalkenes employed according to this invention most preferably are 
prepared by bromination of conjugated diene in the presence of cupric 
bromide. Useful conjugated dienes are those containing 4 to about 12 
carbon atoms such as 1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 
2,4-hexadiene, 2-methyl-1,3-hexadiene, 1,3-octadiene, 3,5-octadiene and 
1,3-dodecadiene. 
Reaction of dibromoalkenes with alkali metal formate according to this 
invention is conducted under conitions such that hydrolysis of the 
dibromoalkene takes place. Such conditions, also referred to herein as 
hydrolysis conditions, include relative proportions of alkali metal 
formate and dibromoalkene, concentration of formate salt in aqueous 
reaction medium, temperature, pressure and time, and are discussed in 
greater detail hereinbelow. 
Preferably, at least about two moles alkali metal formate are used per mole 
dibromoalkene to ensure substantially complete conversion of dibromoalkene 
to alkenediol. Typically, conversion increases with increasing formate 
salt to dibromoalkene molar ratios, and accordingly, ratios in excess of 
about 2:1 are more preferred. Most preferably, the alkali metal formate to 
dibromoalkene molar ratio ranges from about 2.5:1 to about 10:1. Molar 
ratios of less than about 2:1 can be used if desired but are not preferred 
as conversion may be lower than desired. 
Hydrolysis according to this invention is conducted under aqueous 
conditions. Water is used in an amount which is at least sufficient to 
maintain substantially all of the alkali metal formate employed in 
solution and avoid formation of undesirably high levels of formate esters 
during hydrolysis. Preferably, the amount of water is such that the 
concentration of alkali metal formate ranges from about 5 to about 30 wt. 
%. More preferably, this concentration ranges from about 6 to about 18 wt. 
%, with best results being attained from about 8 to about 15 wt. %. Water 
participates in the hydrolysis reaction, with two moles being required for 
conversion of each mole of dibromoalkene to alkenediol based upon reaction 
stoichiometry. The above-described alkali metal formate to dibromoalkene 
molar ratios and alkali metal formate concentrations are effective to 
ensure the presence of at least a stoichiometric amount of water. 
Temperature in the hydrolysis reaction is sufficiently high to ensure 
reasonable reaction rates but not so high as to promote substantial 
decomposition of dibromoalkene starting material. Preferred temperatures 
range from about 80.degree. to about 150.degree. C. More preferably, the 
hydrolysis temperature is about 100.degree. C. 
Pressure in the hydrolysis reaction varies somewhat depending on 
temperature and, in general, is sufficiently high to maintain a liquid 
phase in the hydrolysis zone. Preferred hydrolysis pressure is about 
atmospheric. 
Reaction time varies depending upon reactant proportions, temperature and 
rate of mixing of the reactants, and generally is sufficiently long to 
ensure substantial conversion of dibromoalkene to alkenediol. The 
hydrolysis reactants preferably are agitated in order to increase reaction 
rates. 
Products of the hydrolysis reaction comprise a water and formic acid 
solution of alkenediol and alkali metal bromide. If alkali metal formate 
is used in excess of a stoichiometric amount, in the reaction mixture also 
contains soluble alkali metal formate. Separation of alkenediol from the 
hydrolysis product is preferably accomplished by distillation, although 
extraction, adsorption on active carbon and other suitable techniques also 
can be employed. Following separation of alkenediol, alkali metal formate, 
if present, can be recovered from the remaining hydrolysis product by 
filtration or other suitable solid-liquid separation techniques and 
re-used in hydrolysis. 
According to a more specific aspect of the invention, alkenediols are 
produced according to a series of reactions, including the above-described 
hydrolysis reaction, in which only conjugated diene, oxygen, and water are 
consumed. 
Briefly, the process according to this aspect of the invention comprises 
contacting conjugated diene with cupric bromide under bromination 
conditions to form dibromoalkene, contacting the resultant dibromoalkense 
with alkali metal formate under hydrolysis conditions to form alkenediols, 
and contacting cuprous bromide formed in the bromination step and alkali 
metal bromide and formic acid formed in the hydrolysis step with molecular 
oxygen under conditions effective to regenerate cupric bromide and alkali 
metal formate which can be recycled. If desired, regenerated cupric 
bromide and alkali metal formate can be separated prior to recycle. 
However, the presence of alkali metal formate during bromination does not 
hinder the bromination reaction, and accordingly, it is preferred to 
recycle both salts to the bromination step without separation. 
In greater detail, the bromination step according to this aspect of the 
invention comprises contacting conjugated diene with cupric bromide under 
conditions effective to form dibromoalkenes. The reaction is conducted in 
the presence of an inert liquid medium in which the conjugated diene to be 
brominated is soluble. Suitable media include alkanes such as hexane, 
heptane and octane as well as various other materials which are 
substantially inert to the reactants employed and liquid at bromination 
temperatures, such as acetonitrile and dimethylformamide. Preferably, the 
medium is purified prior to use, for example by percolation through silica 
gel and/or molecular sieves, to remove traces of water and other 
impurities which may promote undesirable side reactions and otherwise 
interfere with the bromination reaction. 
Conjugated dienes suitable for use according to this aspect of the 
invention are those containing 4 to about 12 carbon atoms, specific 
examples of which are identified hereinabove. Gaseous dienes are charged 
under pressure sufficient to solubilize the same in the reaction medium, 
but not so high as to promote substantial oligomerization of the diene, 
although it is contemplated to employ inhibitors capable of retarding 
oligomerization without interferring with the bromination reaction to 
facilitate the use of higher diene pressures. Preferably, gaseous 
conjugated dienes are charged to the bromination zone under pressure of 
about 1 to about 6 atmospheres (about 1 to about 6.2 kg/cm.sup.2) to 
ensure solubilization without the need for oligomerization inhibitors. 
Liquid conjugated dienes can be charged under pressure if desired though 
this is neither necessary nor preferred. 
From the reaction stoichiometry, two moles of cupric bromide are required 
for bromination of each mole of conjugated diene. However, in order to 
avoid promotion of side reactions and formation of brominated alkanes, it 
is desirable to employ the conjugated diene in excess of the 
stoichiometric amount. Preferably, the molar ratio of conjugated diene to 
cupric bromide is at least about 0.52:1. More preferably, this ratio 
ranges from about 0.52:1 to about 5:1, although a substantially greater 
proportion of diene can be used if desired and often gives particularly 
good results in continuous processes. 
Bromination temperatures are sufficiently high to ensure reasonable 
reaction rates but not so high as to promote substantial oligomerization 
of conjugated diene. Again, it is contemplated to employ suitable 
inhibitors to retard oligomerization and thereby facilitate the use of 
higher temperatures. Preferred bromination temperatures range from about 
75 to about 150.degree. C., with best results being attained at about 
100.degree. C. 
In batch processes, the time of the bromination reaction varies depending 
on temperatures, reactant proportions, etc. and generally is sufficient to 
allow for substantially complete conversion of diene to alkenediol. 
Residence time in the bromination zone can be regulated as desired in 
continuous processes. 
Although not required, all or a portion of the alkali metal formate to be 
used in the hydrolysis step can be present during the bromination step if 
desired. The presence of alkali metal formate during bromination does not 
hinder the bromination reaction, and while some formate esters may form, 
this typically is of no consequence because the same are subsequently 
hydrolyzed. Conveniently, a combination of cupric bromide and alkali metal 
formate is added to the bromination zone, although it also is contemplated 
to add cupric bromide separate from the alkali metal formate. In a 
particularly preferred operational mode discussed in greater detail 
hereinbelow, continuous production of alkenediol is accomplished by adding 
an initial charge of cupric bromide and alkali metal formate to a 
bromination zone, subsequently regenerating cupric bromide and alkali 
metal formate from bromination and hydrolysis by-products, and then 
recycling regenerated cupric bromide and alkali metal formate to the 
bromination zone. 
The product of the bromination step comprises solid cuprous bromide and a 
solution of soluble dibromoalkenes in the reaction medium. Alkali metal 
formate, if present in the bromination step also is included in the 
reaction mixture in the form of a solid. Reaction medium is removed from 
the bromination product, preferably by distillation, and the medium can be 
condensed and recycled to the bromination zone if desired. 
The remaining bromination product, comprising dibromoalkene, solid cuprous 
bromide and, if present during the bromination step, solid alkali metal 
formate, then is passed to a hydrolysis zone which is provided with 
sufficient water and alkali metal formate for the hydrolysis step. Of 
course, if the bromination product already contains sufficient alkali 
metal formate for hydrolysis, there is no need for further addition of 
formate salt. Relative proportions of dibromoalkene and alkali metal 
formate and aqueous alkali metal formate concentrations in the hydrolysis 
step are as discussed hereinabove. 
Hydrolysis is conducted by reacting dibromoalkene, alkali metal formate and 
water under hydrolysis conditions, as described hereinabove, to form a 
reaction mixture comprising a water and formic acid solution of 
alkenediol, excess alkali metal formate and alkali metal bromide as well 
as insoluble cuprous bromide. Water, formic acid and a major portion of 
alkenediol are separated from the hydrolysis product, preferably, by 
vacuum distillation so that separation can be accomplished at temperatures 
low enough to avoid promotion of undesirable side reactions, e.g., below 
about 150.degree. C. Subsequently, the recovered water, formic acid and 
alkenediol are further separated into an alkenediol stream and a water and 
formic acid stream, preferably by fractional distillation. Preferably, a 
major portion of the water and formic acid recovered from the hydrolysis 
step is used in regeneration as described in greater detail hereinbelow. 
The hydrolysis product remaining after separation of alkenediol, water and 
formic acid comprises a concentrated slurry of cuprous bromide, alkali 
metal bromide and excess alkali metal formate in alkenediol. Solids are 
separated from the slurry, preferably by filtration, and residual 
alkenediol is removed from the resulting solids, preferably by washing the 
same with a portion of the water and formic acid stream recovered from the 
hydrolysis product. Of course, fresh water and formic acid or other 
suitable wash media, such as lower aliphatic alcohols, can be used if 
desired; however, process efficiency is optimized through the use of a 
portion of the recovered water and formic acid stream as the wash liquid. 
After separation of the wash filtrate, the remaining solids are conveyed 
to a regeneration zone and contacted therein with molecular oxygen in the 
presence of formic acid under regeneration conditions. Preferably, water 
also is present during regeneration. Conveniently, formic acid and water 
used in regeneration are supplied by the water and formic acid stream 
recovered from the hydrolysis product. 
Molecular oxygen is charged to the regeneration zone in an amount 
sufficient to ensure reasonable reaction rates but not so high as to 
create a flammable mixture of oxygen and formic acid or cause oxidation of 
formic acid to carbon dioxide and water. Preferably, oxygen partial 
pressures range from about 20 to about 40 psig. Most conveniently, 
molecular oxygen is supplied to the regeneration zone in the form of air, 
although other sources are contemplated. In addition, one or more diluent 
gases can be charged to the regeneration zone to increase overall pressure 
while maintaining nonflammable levels of oxygen. Suitable diluent gases 
include ethane and other hydrocarbons which are inert to the regeneration 
reactants and remain in the gaseous state under regeneration conditions. 
The amounts of formic acid and, if used, water employed in regeneration are 
at least sufficient to provide for substantial conversion of alkali metal 
bromide and cuprous bromide to alkali metal formate and cupric bromide 
without substantial oxidation of formic acid. Preferably, from about 0.5 
to about 5 moles formic acid are used per mole of alkali metal bromide and 
up to about 1 mole of water is present per mole of formic acid. More 
preferably, the molar ratio of formic acid to alkali metal bromide ranges 
from about 1:1 to about 2:1 and the molar ratio of water to formic acid 
ranges from about 0.005:1 to about 0.5:1. In continuous processes wherein 
formic acid and water for regeneration are supplied by a formic acid and 
water stream separated from the hydrolysis product, the latter can be 
adjusted to provide the desired amounts of water and/or formic acid to the 
regeneration zone with addition of water or formic acid as necessary to 
provide the desired water to formic acid ratio. 
Regeneration temperatures are sufficiently high to ensure reasonable 
reaction rates without promoting substantial oxidation of formic acid. 
Preferred temperatures range from about 80.degree. to about 120.degree. 
C., best results being achieved at about 100.degree. C. 
As a result of the regeneration step, cuprous bromide formed during the 
bromination step is oxidized to cupric bromide and alkali metal bromide 
formed during hydrolysis is converted to alkali metal formate. These salts 
are separated from excess formic acid and water present in regeneration, 
for example by distillation, and then dried. Water and formic acid 
preferably are condensed and recycled to the hydrolysis zone. Dried cupric 
bromide and alkali metal formate preferably are recycled to the 
bromination zone either in solid form or as a slurry in a liquid suitable 
for use as reaction medium in the bromination step.

The present invention gives best results in the continuous production of 
2-butene-1,4-diol such that only 1,3-butadiene, oxygen and water are 
consumed. This embodiment of the invention is described in greater detail 
in conjunction with the drawing. 
To agitated bromination zone 1 containing hexane, cupric bromide and sodium 
formate, and maintained at bromination temperature, is charged 
1,3-butadiene through line 3 under pressure sufficient to solubilize the 
diene in the hexane without oligomerization of diene. 
Bromination product, comprising solid cuprous bromide and sodium formate as 
well as a hexane solution of mixed dibromobutene isomers rich in 
1,4-dibromo-2-butene is passed from the bromination zone through line 5 to 
tower 7. In the tower, hexane is stripped from the bromination product and 
returned to bromination zone 1 via line 9. 
Tower bottoms, comprising cuprous bromide, sodium formate and 
dibromobutenes are passed through line 11 to agitated hydrolysis reactor 
17. Water is added through line 13 and recycle water and formic acid are 
supplied through line 15. 
The reaction mixture is subjected to hydrolysis conditions in hydrolysis 
reactor 17 with the result that 1,4-dibromo-2-butene is substantially 
converted to 2-butene-1,4-diol and 3,4-dibromo-1-butene is converted 
primarily to 1-butene-3,4-diol but with some isomerization to 
2-butene-1,4-diol. 
The hydrolysis product, comprising mixed butenediol isomers rich in 
2-butene-1,4-diol, sodium formate and sodium bromide dissolved in formic 
acid and water, plus solid cuprous bromide is passed through line 19 to 
tower 21 in which water, formic acid and most of the butenediol are vacuum 
distilled. Distillate is passed through line 23 to tower 25 in which water 
and formic acid are distilled. Liquid butenediol is removed from tower 25 
via line 27 to purification and/or storage equipment (not shown). 
Bottoms from tower 21, comprising a concentrated butenediol slurry of 
cuprous bromide, sodium bromide and sodium formate pass to filter 31 via 
line 29. A portion of the water and formic acid recovered in tower 25 is 
added to the filter via lines 33 and 35. 
In filter 31, bottoms from tower 21 are washed with formic acid and water 
to remove residual butenediol. Wash filtrate, comprising water, formic 
acid and a minor amount of butenediol, is returned to tower 21 via lines 
39 and 19. 
Solids from filter 31 are passed via line 37 to line 33 which carries a 
major portion of the water and formic acid recovered in tower 25. A water 
and formic acid slurry of cuprous bromide, sodium bromide and sodium 
formate pass to agitated regeneration zone 41 via line 33. 
Air is charged to the regeneration zone through line 43 and the contents 
are subjected to regeneration conditions to oxidize cuprous bromide to 
cupric bromide and convert sodium bromide to sodium formate. 
The regeneration product is passed through line 45 to tower 47 in which 
water and formic acid are stripped. These are recycled to the hydrolysis 
reactor via line 15. Tower bottoms, comprising cupric bromide and sodium 
formate are conveyed to dryer 49, dried, and then recycled to bromination 
reactor 1. 
The following examples illustrate the present invention, it being 
understood that the same are not to be construed as limiting the scope of 
the invention. 
EXAMPLE I 
To a 300 ml glass pressure bottle equipped with mechanical stirrer, 
thermocouple, gas inlet and pressure gauge were added 34.9 g n-heptane 
followed by 22.3 g (0.10 mole) cupric bromide. The bottle then was placed 
in dry ice and 0.057 mole (3.078 g) 1,3-butadiene were metered into the 
bottle using a wet test meter. The pressure bottle was removed from the 
dry ice and heated to 100.degree. C. with stirring. Heating at 100.degree. 
C. and stirring were continued for 13/4 hours. 
During heating a maximum pressure of 21 psig was attained. By the end of 
the run, pressure had decreased to 8 psig. Based on the rate of pressure 
drop, at least 77 mole % of the 1,3-butadiene was consumed during the 
first 30 minutes of heating. 
Following heating the reaction product was analyzed by gas chromatography 
using a 10% DEGS-PS, 6 foot glass column. Analysis showed that 0.0492 mole 
dibromobutenes were produced. This corresponds to a 98 mole % yield based 
upon the limiting reagent, cupric bromide. Distribution of dibromobutene 
isomers was determined by gas chromatography, again using a 10% DEGS-PS, 6 
foot glass column. Results were as follows: 67% 
trans-1,4-dibromo-2-butene, 12% cis-1,4-dibromo-2-butene, and 21% 
3,4-dibromo-1-butene. 
EXAMPLE II 
The procedure of EXAMPLE I was repeated except that the initial amount of 
1,3-butadiene was decreased to 0.0404 mole such that the diene was the 
limiting reagent. 0.0379 mole dibromobutenes were produced corresponding 
to a 94 mole % yield based on the initial charge of 1,3-butadiene. Isomer 
distribution was as in EXAMPLE I. 
EXAMPLE III 
Bromination was conducted substantially as described in EXAMPLE I. The 
product was filtered to remove cuprous bromide and then stripped of 
heptane solvent. Analysis of the product as in EXAMPLE I showed 79% 
1,4-dibromo-2-butene and 21% 3,4-dibromo-2-butene. 
15.5 g (0.0725 mole) of the dibromobutenes produced in the bromination step 
were added to a solution of 10 g (0.147 mole) sodium formate in 50 ml 
water in a large glass flask. The hydrolysis mixture then was heated at 
the reflux temperature for 21/2 hours. After heating there resulted a 
clear, slightly yellow solution containing a few small droplets of a 
second phase. Analysis of the solution by gas chromatography according to 
the procedure of EXAMPLE I showed no dibromobutenes and an 88 mole % yield 
of butenediol isomers based upon the initial dibromobutene charge. The 
distribution of butenediol isomers was 92% 2-butene-1,4-diol and 8% 
1-butene-3,4-diol. 
EXAMPLE IV 
The procedure of EXAMPLE III was repeated except that in the hydrolysis 
step only trans-1,4-dibromo-2-butene was used and the sodium formate to 
trans-1,4-dibromo-2-butene molar ratio was 4.4:1. Analysis of product 
showed a 94 mole % yield of butenediol isomers based upon the initial 
dibromobutene charge. Isomer distribution was 93% 2-butene-1,4-diol and 7% 
1-butene-3,4-diol. 
EXAMPLE V 
Regeneration of cuprous bromide and sodium formate from by-products of the 
bromination and hydrolysis steps was demonstrated as follows. To a 
jacketed, 1 liter, titanium, stirred autoclave equipped with reflux 
condensor and gas inlets were added 42.9 g (0.30 mole) cuprous bromide, 
30.9 g (0.30 mole) sodium bromide, 13.8 g (0.30 mole) formic acid, 81.6 g 
(1.2 moles) sodium formate and 300 g water at ambient temperature 
(22.degree.-25.degree. C.). Temperature then was increased to 100.degree. 
C. and a gaseous mixture of 80 vol. % ethane, 15 vol. % butadiene and 5 
vol. % O.sub.2 was charged to the autoclave at a rate of 120 STP 1/hr. 
After 30 minutes the contents of the autoclave were analyzed for copper 
(II) ions by iodometry. Analysis showed Cu(II) corresponding to a 90 mole 
% yield of cupric bromide based upon the starting amount of cuprous 
bromide.