Walter Reppe
Pioneer in Acetylene Chemistry
ColorantsHistory.Org
Walter Reppe (1892-1969)
Photo:  www.euchems.org
Walter Reppe was born in Göringen near Eisenach, Germany on July 29, 1892.  In 1911 Reppe began his science studies at the University of Jena where he
excelled in chemistry.  After World War I, he resumed studies in Munich under the supervision of Kurt Heinrich Meyer and received a Ph.D. in 1920.  In
1921 he joined the main laboratory of Badische Anilin und Soda Fabrik which would soon become part of I.G. Farbenindustrie. His early research involved
the dehydration of formamide to produce prussic acid (hydrogen cyanide). In 1928 he started research on acetylene reactions under high pressure, a field
which became widely known as 'Reppe chemistry'. He studied the vinylisation of alcohols, carboxylic acids and nitrogen compounds and developed the
technology to commercialize the processes.

BASF warned Reppe in 1928 about the danger of working with acetylene under pressure. Most countries at that time prohibited such experiments and in
Germany, the Acetylene Ordinance only allowed handling acetylene below 1.5 atm.

But Reppe wanted to use the gas to produce small organic molecules, monomers, for experiments in the newly emerging field of plastics.  To obtain
official permission for his high pressure experiments he conducted experiments on a larger scale in Ludwigshafen in the 1930s. His goal was to safely
handle acetylene at pressures up to 25 bar. For this purpose he studied the decomposition of acetylene in ignition experiments.  He learned the
conditions under which the decomposition was delayed to prevent an explosion.  Dilution of acetylene with inert nitrogen gas and the use of stainless
steel, walled reactor tubes were key discoveries in working safely with acetylene at pressures up to 200 atm.

Reppe now began to synthesize a wide variety of different vinyl compounds.  Contrary to the scientific skeptics, he succeeded in producing vinyl ether
from acetylene and alcohols
.  The technique known as "ethynylation" was suitable for the commercial scale and in the years that followed Reppe focused
on other reactions such as "carbonylation" and finally on the "cyclic oligomerization" of acetylene. The various pressurized reactions of acetylene resulted
in a large number of new chemical compounds with diverse applications.

A patent was filed in 1939 for one of the most significant derivatives of acetylene chemistry: polyvinylpyrrolidone (PVP). It was initially used as a blood
plasma substitute and later in many applications in medicine, pharmacy, cosmetics and industrial production.

The vinyl ether production facility went into operation in September 1939, followed four years later by the butanediol plant. Since Germany was cut off from
key raw materials such as natural rubber during World War II, butanediol was used to produce the synthetic rubber Buna.

The bombing of Ludwigshafen forced Reppe to transfer in September 1944 to the inorganic facility at Gendorf in Upper Bavaria, where he conducted olefin
high pressure experiments in a smaller laboratory.  He was detained by the U.S. Army in June 1945 and subjected to rough interrogation about his
research. The valuable acetylene technology was considered as reparations for the war.  

Colonel Ernest Gruhn, director of the Joint Intelligence Objectives Agency in Washington, tried to bring Reppe to the U.S.  Reppe said he was insulted
when offered a contract to work for only $6 per day.  He was then interned in November 1945 at "Camp Dustbin" in Oberusel, near Frankfurt, where he was
ordered by the military to document the acetylene technology.  Camp Dustbin was the former "Durchgangslager der Luftwaffe" or "Transit Camp of the
Luftwaffe" which the Germans used to interrogate captured Allied airmen.













During internment, Reppe went on a hunger strike and was forced to do menial work like cleaning toilets.  He was upset with reports in the American press
saying he was a Nazi.  He said he only joined the party in 1944 to keep his group of young chemists out of the special command of General Walter von
Unruh, known as "General Heldenklau", which replaced officers and soldiers on the front lines.  He was not implicated in any war crimes at Nuremberg.

In 1946 the U.S. Department of Commerce sponsored a mission of American chemists to Germany to learn more about acetylene chemistry.  The General
Aniline and Film Corporation (GAF), a former subsidiary of I.G. Farben, had acquired the acetylene patents before the company was seized as an enemy
asset in 1942.  GAF chemists Dr. Abraham O. Zoss and the late Dr. Donald L. Fuller, based at the Easton, Pennsylvania research laboratory, spent several
months in Germany visiting plants and laboratories in Ludwigshafen and Oppau and interviewing scientists.  

Zoss spoke with some of Reppe's chemists in his laboratory to learn about his personality.  Hearing that Reppe loved cigars, Zoss brought some to warm
him up for questioning.  The interview took place in Reppe's prison cell in Dustbin.  Reppe was very pompous and conceited.  When Zoss mentioned how
impressive he found his staff in the research laboratory of about 100 scientists, Reppe stopped him, raised his hands up front and spat out "that was all my
work - they were just my hands."  Reppe's abrasive personality would later keep him from becoming the head of BASF.

Reppe was released from internment at the Dachau military hospital in September 1947.  He narrowly escaped death on July 28, 1948 when a railcar loaded
with 30 tons of dimethyl ether, used in making acetic acid and dimethyl sulfate, exploded inside the factory gates of Ludwigshafen.  Reppe had smelled
something and got up from his desk seconds before the blast which studded his chair with yard-long glass shards.  The explosion and resulting fire killed
207 people and injured 4,000.  A even deadlier explosion occurred in the nearby Oppau plant in 1921 when workers used dynamite to pry loose 4,000 tons
of caked ammonium nitrate.  The blast killed 561 people and leveled houses four miles away.  Reppe said he was sleeping in bed when "Oppau in die Luft
flog" (when Oppau flew in the air).   















Reppe authored the pioneering work titled
New Developments in the Field of Chemistry of Acetylene and Carbon Monoxide which was published by the U.S.
government in 1949.  He was named research director of BASF and joined the Board of Management.  He visited the United States in 1954 and was a guest
speaker at the 150th meeting of the Western Connecticut Section of the American Chemical Society.  He gave a speech titled "Carbonylation of Acetylene
and Acetylene Derivatives" and discussed the safety methods used to handle acetylene.

Reppe had developed the carbonylation process in 1939, in which acetylene was reacted with carbon monoxide and water in the presence of a nickel
carbonyl catalyst.  The technology attracted the interest of the Dow Chemical Company since acrylic acid and its esters were important monomers for
resins and fibers.  The Dow Badische company was formed in 1959 as a 50-50 joint venture of Dow and BASF to produce acrylic acid, butanol and
caprolactam in Freeport, Texas.  BASF benefited from Dow's knowledge of the U.S. market.














BASF later purchased Dow's share of Dow Badische.  Today, acrylic acid is manufactured by the more economical propylene oxidation process.

Reppe retired in 1957 and died in Heidelberg on July 26, 1969.  He was survived by a son, Hans Gerhard Reppe, who also worked for BASF as a chemist,
with 19 patents awarded in the 1960s.

Butanediol, like many different vinyl ethers, remains an important intermediate product for BASF. The butanediol plant in Ludwigshafen, the largest of
BASF's facilities for the production of butanediol, still operates six reactors built under Reppe's supervision. BASF's annual worldwide production capacity
is currently running at 585,000 metric tons of butanediol equivalents.














































































An excerpt, with minor editing, of the interview of Walter Reppe in 1945 by the Technical Industrial Intelligence Committee, published in the FIAT Final
Report No. 273, is presented below:

"Dr. J. W. Reppe, director of I.G.Farbenindustrie and head of the Hauptlaboratorium at Ludwigshafen, was interviewed with respect to his contribution to
the German war effort. He played an important part in the last war (1914-1918) in developing the German process for making mustard gas but has had
nothing to do with war gases in this war.

His principal contributions to this war were stated to be:

a. Synthesis of a substitute for blood plasma called Periston
b. An adhesive that makes Buna adhere to fabric and is called Korosin — it formed an essential part of the German synthetic rubber program
c. New reactions in the synthesis of butadiene

Dr. Reppe and his co-workers have developed new processes that involve novel reactions of the acetylenes, olefines and reactions of metallic carbonyls;
these developments will probably be of future industrial importance and are discussed below along with other reactions described by Dr. Reppe.

The industrial success of the above acetylene chemistry depended first on the development of safe method and means of handling acetylene (C2H2)
under pressure, and for some of its reactions, and the safe use of large quantities of metallic acetylides — more especially that of copper. Reppe’s
laboratory has acetylene piped at 30 atm. pressure and plans are made to use it at pressures of 150 atm. Basic investigations of explosions in compressed
acetylene in the absence of oxygen in small bombs showed that the pressures developed to 10 times its initial partial pressure in a mixture and that the
large scale application depended (1) on the provision or equipment to withstand such possible pressure increases and (2) restricting possible explosions
to rather small volumes. This latter requirement was met in small-scale apparatus by using for a required delivery of acetylene instead of a single pipe a
plurality of smaller pipes about one inch in diameter through which more than a given output of acetylene was continuously circulated by looping the lines
back to the suction-side of the large capacity compressor and by using one-way bicycle-tire valves at spaced intervals in the lines. In larger installations,
the 4-6 inch pipelines were completely filled throughout their length with pipes of small diameter (about 5-10 mm.) to form a sort of honeycomb structure
throughout their extent. The latter has worked so well that, in the large plant for manufacturing about 4500 tons per month of butin-2-diol from acetylene
and formaldehyde at Ludwigshafen, of the three explosions experienced, only the lines were burnt through in a very small area without further trouble.
After these explosions, the tubes were carefully cleaned and reassembled.

Explosions are prevented in large masses of metal-acetylide catalysts by keeping them wet. They are formed in situ by depositing a salt of the required
metal, for example the nitrate, on silica-gel pellets and heating the same for conversion of the nitrate to the oxide and thereafter treating them with
acetylene under pressure. The only acetylide catalyst in commercial plants is made by reacting copper oxide with acetylene in situ (see butin-2-diol
process).

Acetylene Chemistry.

Reactions of Alcohols and Acetylenes.

Dr. Reppe discussed the well-known reaction between acetylene and alcohols and stated that the reaction was quite general for both aliphatic and
aromatic alcohols including primary and secondary alcohols, mercaptans an phenols. Potassium hydroxide is employed as the catalyst. Ethers and esters
and secondary amines also react with acetylene under pressure. For example, the reaction between methyl alcohol and acetylene goes very smoothly at
about 200°C to give methyl vinyl ether in the presence of KOH:

                                                                                    CH3OH + HCCH → CH3O - CH = CH2

Methyl vinyl ether is hydrolysable at 180°C with water to give acetaldehyde and methyl alcohol and the latter can be returned to the process.
This production of acetaldehyde without a mercury catalyst was considered important for German industry because 2 kgs of mercury are lost in the
production of a ton of Buna; however a plant was never built.

Another important reaction of acetylene and an alcohol is that with phenol, also employing KOH as the catalyst, which gives first phenyl vinyl ether that can
convert to vinyl phenol. Depending upon the amount of acetylene substituted on the benzene nucleus, will depend the characteristics of the polymer
made from the resultant oxy-styrenes wherein the vinyl groups are in the ortho and para position to the hydroxy group.  To make a resin of the Bakelite,
phenol is reacted with acetylene at a pressure of 10 atm.

Organic zinc salts, for example the naphthenate, are good catalysts for the phenol-acetylene reaction and they can give substituted oxy-styrenes that are
solids.

Although the mercaptans, as mentioned above, react with acetylene to give products analogous to those derived from the oxygen alcohols, the products
are malodorous and are not of particularly practical value.

Korosin, the adhesive for synthetic rubber, is made by reacting isobutylphenol with acetylene. This was considered an indispensable development in the
German synthetic rubber program as this material bound the synthetic rubber to the fabric.  It also assists in producing a tire that does not get hot in use.
In this case the acetylene does not form an ether but substitutes for hydrogen on the benzene ring under the influence of zinc naphthenate as catalyst.
The reaction takes place in the liquid phase (Rieselverfahren) forming the hypothetical monomer shown below which, however, polymerizes as formed:









At Ludwigshafen, the I.G. Farbenindustrie has a small plant for the production of vinyl ether especially from methyl alcohol and acetylene. The reaction was
carried on in liquid phase at 15 to 20 atm. pressure of acetylene which was delivered to the reaction vessel as a 50-50 mixture with nitrogen; the total
pressure in the system was thus about 30-40 atm. The compressors wore of the vertically reciprocating piston type and the connecting rods were
enclosed in a transparent case to prevent ingress of dust as a precaution against friction and possible explosion that the presence of dust in the cylinder
would cause. The compressors were of the usual type and were capable of delivering 100 and 180 cubic meters per hour.

Reactions of Aldehydes with Acetylene.

Such aldehydes as formaldehyde, acetaldehyde, propion-aldehyde etc. can be reacted with acetylene under pressure in the presence of metallic
acetylides to form unsaturated alcohols. Either one or two molecules of the employed aldehyde can react with the acetylene and the so-formed alcohols
have as many carbon atoms as are present in the reacted reagents, for example with acetylene and formaldehyde, there can be prepared both:

                                                                               (1) Propargyl Alcohol:  HC = C - CH2OH

                                                                          (2) Butine-3-diol-1,4:  HOCH2 - C = C - CH2OH

The reaction is one of the moat promising developments of Dr. Reppe and his co-workers. The above alcohols are made by introducing a mixture of
reaction products with sufficient of a 35% aqueous solution of formaldehyde to provide a 10% solution of the latter in concurrent flow into a tower that is
packed with copper acetyilde (10-12%) deposited on baked silica gel pellets. The catalyst is prepared by depositing CuO (Cu(NO3)2 and roasting) - it may
contain some bismuth also - and treating with acetylene in situ in the contact vessels in the presence of water at 60-70°C. The reaction may be controlled
to make up to 70-80% of the product as propargyl alcohol, but the usual procedure makes 92% of said butinediol and 4% propargyl alcohol. The latter is
recycled when only the diol is wanted. The reaction conditions employed are 5 atm. pressure and 100°C. The acetylene is employed in excess and is dry
upon entering the process; it therefore evaporates water sufficiently to remove the exothermic heat of reaction. The outlet gaseous mixture from the
reactor should be water-vapor and acetylene in the ratio of respectively about 4 to 1.

A plant has been running at Ludwigshafen for two years at a capacity of 4500 metric tons per month of butinediol. In this plant the acetylene is compressed
in two stages to 6 atm. with water-ring centrifugal compressors and the compressed gas (without dilution by nitrogen) is piped to the honeycomb pipes
described above. There are 6 reactors (1.5 x 18 m) designed for 50 atm. pressure which however operate at the above 5 atm only. They are lined with
stainless steel (V4A) and have each a volumetric capacity of 20 cubic meters of catalyst containing 2000 kg. of copper acetylide. The inlet solution of
formaldehyde is dripped (Riesel verfahren) through the tower at the rate of 10 cubic meters per hour concurrent to a stream of acetylene of 1 cubic meter
per hour. The reaction being highly exothermic, the only heating employed is heat exchange in the formaldehyde feed lines. The Leistung is 1 ton of
butinediol per cubic meter catalyst per day. The outlet solution from the reactor is distilled to recover 10% unreacted formaldehyde and produced
propargyl alcohol which are recycled. Based on formaldehyde, the yield of butinediol is about 98%. There were some difficulties at the beginning of the top
of the reactor which were overcome by diluting the formaldehyde solutions, as above described. There have been acetylene explosions in the pipes near
the control valve to the reactor, but the only damage was to burn a small hole in the pipe.

The reaction solution contains about 30% butinedioi.. By evaporation and crystallization from ethyl acetate, the butinediol can be recovered in crystalline
form; the butinediol as prepared above in aqueous solution can be hydrogenated while still in such solution to butenediol-1,4 and also to butanediol-1,4 by
means of a nickel or copper catalyst at 200-300 atm. by means of circulated hydrogen. The conversion of butinediol-1,4 to butanediol-1,4 by hydrogenation
is 96%.

The butanediol-1,4 (n-butylene glycol) can be recovered from the aqueous solution and can be dehydrated in one step to butadiene over a phosphate
catalyst as developed by I.G. Farben in 1926. The butanediol is now made at Ludwigshafen for 60 pfg. per kilo and it is expected to reduce this to 40-50 pfg.
per kilo.

However, it is preferable because of higher yields and for other reasons according to Dr. Reppe, to dehydrate the butanediol to butadiene in two steps:
that is, first to tetrahydrofurane and then the latter to butadiene.

Tetrahydrofurane appears to be an important new building block in synthetic chemistry. It is a good solvent for many types of compounds including also
such high polymers as polyvinylchioride, polyvinyl carbazol, natural rubber and Buna. It enters many reactions. Adipic acid can be made therefrom (see
below). In the above aqueous solution of 30-35% butanediol-1,4, obtained by hydrogenation of the reaction product of formaldehyde and acetylene, the
former can be dehydrated to tetrahydrofurane in said solution by the addition of a small amount of H3P04 and maintaining the pH at least 2 and distilling the
mixture at a temperature of about 260-300°C and a pressure of 60-100 atm; the THF (tetrahydrofurane) is easily volatilized under these conditions and is
quantitatively produced. The Na and Ca ions in the solution added for control of the pH value are substituted by H ions and by ion-exchange media
(Wolfatite).

The THF can then be converted at 260-280°C to butadiene by means of a phosphate catalyst; it can also be treated with metallic carbonyls and converted to
adipic acid.

Butanediol-1,4 is also the starting product for the new blood plasma substitute. By oxidation of its hydroxy groups to aldehydes by simple spraying over a
Cu catalyst at 200°C, by the well-known Cannizarro reaction, there is produced gamma hydroxybutyric acid and butyrolactone which the end-product of the
reaction, and gamma butyrolactone reaction with liquid ammonia at 250°C gives alpha pyrrolidone as described by Prof. Sprath of Vienna, and in
accordance with the following equations:



























Conversion of pyrrolidone to its potassium salt and the latter’s reaction with acetylene, similarly to the known preparation of vinyl carbazole, gives a N-
vinylpyrrolidone which is the monomer of Periston.

Vinyl pyrrolidone can be polymerized to Periston by aqueous solution of NaHSO3 or by oxidation with H2O2 at a temperature of 70-80°C; the H2O2 is the
catalyst and is employed in amounts of 0.05 to 1% plus NH3 to the extent of one-quarter to one-half of the employed H2O2 which determines the degree of
polymerization. Periston is neutral, has a high viscosity and is broken down in and eliminated by the human body. It has been used in thousands of German
soldiers, but the Allied medical experts have not accepted its use.

















By reaction of NH3 or amines with THF, it is converted to pyrrolidine and its N-substituted products; these products are valuable in insecticides and in
vulcanization acceleration. The dehydrogenation or pyrrolidine gives pyrol. The structure of pyrrolidine is:






Propargyl alcohol which is made when one mole of formaldehyde adds to acetylene has promising uses. When oxidized with air at 30°C in the presence of
copper chloride, it forms hexadiindiol 2,4-diin,-1,6 diol.

This latter compound, on incomplete hydrogenation, yields two isomers of hexadienol:

                                                                                     a) Hexadienediol, 2,4 diene,1,5 diol

                                                                                     b) Hexadienediol, 2,4 diene,1,6 diol  

No use is known for the compound (a), but the compound (b) can be converted to either of two Nylon building blocks. It is hydrogenated to hexanediol-1,6
and it then can be oxidized with nitric acid to adipic acid on the one hand, or said diol can be partially oxidized to give epsilon hydroxy caproic acid that
easily dehydrates to caprolactone; reaction of the latter with NH3 gives epsilon caprolactam which has the following structural formula:"

































References:


1) E.B. Peck and Irvin H. Jones, "Interview with Dr. J.W. Reppe, I.G. Farbenindustrie, AG", FIAT Final Report No. 273, October 2, 1945,
http://www.fischer-tropsch.org/primary_documents/gvt_reports/FIAT/fiat_273/fiat_273_toc.htm, accessed April 20, 2009

2) Robert J. Baptista and Anthony S. Travis, "I.G. Farben in America: The Technologies of General Aniline and Film", History and Technology, Vol. 22, No. 2,
June 2006, pp. 187-224.  An unabridged version is available online at
http://colorantshistory.org/IGFarbenAmerica.html.

3) Michael Lang, "Tradition of Ideas:  Reppe Chemistry", http://www.basf.de/en/intermed/news/topstory/archiv/reppe-chemie.htm, accessed April 20, 2009

4) "1925-1944:  New Forms of High Pressure Synthesis", http://www.basf.com/group/corporate/en/about-basf/history/1925-1944/index, accessed April 20,
2009

5) Peter J.T. Morris, "Ambros, Reppe and the Emergence of Heavy Organic Chemicals in Germany, 1925-1945", in Determinants in the Evolution of the
European Chemical Industry, 1900-1936 by A. S. Travis, H.G. Schröter, and E. Homburg, Springer, 1998, pp. 89-122

6) Werner Abelshauser, German Industry and Global Enterprise: BASF : The History of a Company, Cambridge University Press, 2004

7) "Gerade kein Dummkopf", Der Speigel, 37/1948, September 11, 1948, http://wissen.spiegel.de/wissen/dokument/dokument-druck.html?
id=44418801&top=SPIEGEL, accessed April 22, 2009

8) "Speaker Discusses Uses for Acetylene", Bridgeport (CT) Post, November 17, 1954

9) "Catalog of Catastrophe", Time, December 17, 1984, http://www.time.com/time/magazine/article/0,9171,923800,00.html, accessed April 22, 1984

10) "Walter Reppe", http://en.wikipedia.org/wiki/Walter_Reppe, accessed April 20, 2009

ColorantsHistory.Org thanks John Deutsch for contributing the historic photos of the I.G. Farben Ludwigshafen plant.  Dr. Abraham O. Zoss is thanked for
sharing information about his meeting with Walter Reppe in 1946.
Reppe explains the synthesis
route for polyvinylpyrrolidone.
Photo:  www.basf.com
BASF butanediol unit today with the
reactors built under Walter Reppe in 1943.
Photo:  www.basf.de
Reppe chemistry for the synthesis of 1,4-butanediol and N-vinylpyrrolidone.
Source:  "IG Farben in America:  The Technologies of General Aniline & Film", 2006
Copyright © 2009 by ColorantsHistory.Org.  All Rights Reserved.
World War II era scenes of the Ludwigshafen plant of I.G. Farben and the acetylene pilot plant.  
Photos courtesy of John Deutsch.  Click to enlarge.
"Camp Dustbin" in Oberusel where
Reppe was interned with other
German scientists.  Click to Enlarge.
"Walter Reppe: Pioneer in Acetylene Chemistry"
by Robert J. Baptista, Updated June 21, 2009
Click here for list of 1600 German and Austrian scientists
interrogated, including Reppe and Wernher von Braun
Reppe (2nd from right) meets with Dow Chemical
representatives including Dr. A.P. Beutel (right)-ca. 1955.
Photo courtesy of Brazoria County Historical Museum.
Click to enlarge.
                                           Explosion at Oppau 1921                                                          Explosion at Ludwigshafen 1948.  
   Photo:  http://www.reimerei.net/Oppauammoniak_(FRB).htm             Photo:  http://www.hemshof.info/sites/hemshof_geschichte.htm
                                                              Reppe survived both explosions.  Click to enlarge.
How Smoking Was Banned at the BASF Laboratory
Click Here for Rare Film of Ludwigshafen Explosion in 1948
New-"Process Technology in the Third Reich:  The Case of IG Farben and Buna", by Peter Morris, Research
Director-Science Museum, London.  A Lecture Presented at the Oxford History of Chemistry Seminars, May 28, 2009.