Ι / 3EÏ C
S IT» Ι Ε Ο I - Α . X-
F
E Α.Ί·
Metal
"CX Κ Έ
Organic
Organometallics From miracle plastics to jet fuels, the organometallics seem to have a waiting J. Ν 1900, Victor Grignard d e scribed the first of the organomagnesiuni halides—Grignard reagents. I n 1957, boron hydrides are power ing j e t bombers. I n a nutshell, that seems to be the story of metalorganic compounds. Some of the first ones to be discovered a r e still going strong, while new ones a r e being developed to fill the needs of the jet age. Grignard reagents prob ably got their biggest commercial boost in the manufacture of silicone resins. Also, the reaction of Grig nard reagents with inorganic halides is helping give Grignards a new look. Trialkyl phospines and perhaps phosphine oxides a r e believed to be in commercial production a n d alkyl and aryl tins also m a d e by this method. New drugs use their share of Grignards, too. A partial list utilizing t h e Grignard reactions in cludes cortisone, methyl testosterone, vitamin A, and atropine. While j e t plane fuels arc a big factor in the commercial develop ment of boron hydrides, there a r e signs which point u p the fact that development in the boron hydride field m a y someday be independent of military stimulus. O n e such area of great promise is in pharmaceutical applications. Research is now under way to modify highly toxic boron hydrides, so that the compound is specific in toxicity toward various parasites, without being harmful to the host. Of course, with increas ing applications of boron hydrides, quick a n d easy methods of deter mination of various boron compounds must be devised. Gas phase chro matography appears to be one answer. Some experimenters have gotten best results using a Celiteparaffin oil partition column, al though they were able to resolve the 44 A
common volatile boron hydrides on Celite-tricresyl phosphate a n d Celite-octoil S columns. Some com pounds a r e unstable—e.g., pentaborane—on certain column mate rials, but proper and specific column materials c a n be found. T h e boron hydrides a r e rela tively noncorrosive a n d c a n be handled in most common materials of construction Diborane has been handled in steel, stainless steel, brass, copper, lead, Teflon, a n d Kel-F equipment. P e n t a b o r a n e m a y be handled in steel, nickel, a n d Monel equipment. Another organometallic —trimethylaluminum—can also be handled in equipment m a d e from most common materials of construc tion, including aluminum, copper, and carbon steel. However, rubbers and certain plastics react with tri methylaluminum. THOMAS D.
WAUGH,
A r a p a h o e Chemical C o . C H A R L E S J.
If there's one reaction that's been thoroughly studied, its the reaction of ethylene u n d e r pressure with alu m i n u m a n d aluminum chloride. During t h e period 1935-1937, Hall and Nash reported that aluminum chloride in the presence of ethylene and aluminum metal is transformed into a true organometallic compound comparable to a Grignard reagent (indeed, these workers came re markably close to the work Ziegler was later to do, without realizing it). T h e classical studies of Hall a n d Nash were extended by RuthrufT in 1942 when he showed that the reaction of an olefin such as ethylene, with aluminum, aluminum chloride, and hydrogen would produce alkylaluminum compounds. This time Ruthruff came close to duplicating Ziegler's results, without realizing it. Reactions and Uses
RHEES
Both trimethyl- a n d triethylaluminum a r e highly flammable
American Potash & Chemical Corp.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Triethyl- and Trimethylaluminum
MARSEL,
New York University RAYMOND C
market
Commercial sodium process f o r trimethylor triethylaluminum. Commercial aluminum powder is treated with ethyl chloride o r methyl chloride t o p r o duce the correspond ing alkylaluminum sesquichloride. This is m e t e r e d a l o n g with sodium into another agitated reactor where triethylaluminum is f o r m e d a n d r e m o v e d along with the b y - . product aluminum a n d salt. Final purifica tion is e f f e c t e d b y a d d i t i o n o f a small quantity of sodium
Methylchloride or Ethylchloride \
Aluminum /
Sodium Feed Tank
Alkylaluminum Sesquichloride Reactor
Methylchloride or Ethylchloride \ Trialkyl Aluminum
Recovered Dialkyl Aluminum Chloride
Reactor
Crude Alkyl Aluminum
Byproduct NaCI, and Aluminum
Byproduct NaCI
Pure Trialkyl Aluminum
Here's How They're Mode
Handling of Organoaiuminum Compounds
RI + Al -~ RA1I2, R2A1I, R3
V a l v e s (preferably Teflon packed) Stainless steel Brass
2EtMgBr + A1C13-
Eta
° • Et3Al.Et20
Îh
° . R3Al.Et20 RNa + AlCU CH 2 =CH 2 + AlCls + Al • EtAlCl2 pressure E t 2 A i a
Pipelines a n d Containers
polymers of ethylene Black iron, mild steel Copper Pressure vessels Dip tubes
4.
EtQ / +A1 MeCl\
Gloves, flexible leather glove with large wrist gauntlet W o v e n arm guards (optional) Goggles, coverall t y p e , glass preferable Clothing, loose-fitting denim pants and jacket, p r e f e r a b l y flameproofed
liquids that ignite spontaneously in air. T h e y react with water rapidly and with almost explosive violence. T h e reaction with alcohols is exothermic but not violent and can be controlled to give alkoxides. Similarly, the reaction with oxygen or air can be controlled to give alkoxides and in the case of the higher alkyl derivatives of a l u m i n u m this reaction leads to fatty alcohols. Ziegler has shown that triethylaluminum can be treated with ethylene u n d e r pressure to increase the average chain length to 12 or 14 carbon atoms. T h e production of tetraethyllead has been reported by electrolysis of triethylaluminum in the presence of a lead anode. T h e aluminum metal produced at a cathode is reconverted to triethylaluminum by reaction with ethylene and hydrogen. Triethylaluminum is stable at room temperature but disproportionates above 100° C. to diethylaluminum hydride and ethylene. This hydride can also be prepared from diethylaluminum chloride and sodium hydride. Trimcthylaluminum is stable u p to about 250° C. and does not decompose smoothly to a hydride. This latter c o m p o u n d can be prepared from dimethylaluminum chloride and sodium or lithium hydride. Sodium aluminum tetraethide or the tetramethide may be formed by the reaction of sodium or an alkylsodium compound with the corresponding trialkyl a l u m i n u m .
° C · • Me2AlCl, MeAlCl2
Me2Al CI -J Et,Pb + Aids — Et 2 Aia, EtAia 2 Et3Al (trace)
Personnel Protection 1. . 2. 3.
75
CH3C1 + Al(Cu)
a
NaCl
"'° 0 c l ^ V e . EtΑΐα 2 , Et2AlQ 7S c · Me2AlCl2, Me2AlCl EtjAl
Na(K)
Me3Al EtBr + Al Me s ( 7:3 )
, — • Et2AlBr autoclave, 120-140° C. 1 hour 6EtCl + M g i Al 2 -2Et 3 A13MgCl 2 3CnH2„ + Al + A1X3 + V/Ά
Al + 3Chi=CH 2 + 1.5H2
g g g £ g
•
(C„H2nl)2 A1X •
'
120
° C ' . Et3Al press. 120° C
A1 + 3 isobutylene + 1.5 H2
.
press.
3(CH3)2CH=CH2 + EtjAl
(CHj^CHCH^aAl
and Here Are Some of Their Reaction Use» Uses and Reactions of Organoaluminum Compounds RjAl + TiO, - CHj=CH 2 — Polyethylene TiCl3 (olefin) (polyolefin) éEtsAl + 3Pb (anode)
eleCt
' , 3Et,Pb - 4A1 J H2 CIi2 ;: =Cri2
t
EtsAl
1— Et2AlH + CH 2 =CH 2
2Et2Al + A1C13 — 3Et2AlCl 3 N a H . 3Et2AlH EtsAl + 3Na — Et^AlNa 4Et3Al + 3Na — 3NaAlEt4 + Al Reducing agent electroplating Grignard-type reactions, Et2A10CEt2, Et3COH As igniters for rocket fuels
In the sodium reaction one half of the aluminum is lost. Organoaiuminum compounds undergo complex formation with a variety of materials; thus complexes
with ethers, thioethers, amines, and phosphines are known. T h e reaction with carbon dioxide, ethylene oxide, and other reactants commonly used with Grignard reagents is not
Organoaluminum Compounds—What Are They Like? Trimethylaluininum
Triethylaluminum
Form Color
Liquid Clear, colorless
Liquid Clear, colorless
Molecular weight Boiling point, ° C. Melting point, ° C. Density, g . / m l . Pounds/gal. H e a t of combustion
72.07 122 IS 0.752 6.25 1 0 , 5 0 0 cal./g.
114.15 194 - 52.5 0.84 7.02 1 8 , 1 0 0 B.t.u./lb.
Methylaluminum Sesquichloride
Ethylaluminum Sesquichloride
Liquid Liquid Straw colored Straw colored to clear to clear 205.35 246.38
VOL. 49, NO. 12
•
DECEMBER 1957
45 A
Fighting and Prevention of Organoaluminum Fire· 1.
Prevention a.
b.
2.
Sufficient valves to isolate leaks and prevent large spill Lines arranged so that hot lines can be cleaned b y pressure or vacuum before disconnection Extinguishers
a. b. c. d. e.
Water fog Carbon dioxide Dry chemical Sand, vermiculite Do not use carbon tetra chloride or a fire hose with a stream of water
smooth nor can the products always be clearly denned. For example, triethylaluminum and carbon di oxide give Et2AIOCEt 2 initially but continued reaction gives triethylcarbinol; the reaction with sulfur di oxide gives sulfinic acids. T h e interest in commercial pro duction of trimethyl- and triethyl a l u m i n u m is d u e partially to the ex amination of these materials as fuels in j e t engines. Because of their spontaneous flammability, trimethyla n d triethylaluminum have been successfully tested for flame-out pre vention in the ram-jet engine by the Wright Aeronautical Division of the Curtiss-Wright Corp. Because of its relatively high melting point (15° C ) , triethylaluminum has been used with amounts of trimethyla l u m i n u m from 10 to 2 5 % , to depress the freezing point. Trimethyl- and triethylaluminum have also been used in combination with various jet fuels at the 15 to 2 0 % level, to provide for rapid ignition of the latter at high altitudes. Considerable other work in the field is going on in connection with ram-jet, turbo-jet, drones, etc., but at the present time is of a confidential nature. J. F. N O B I S
U. S. Industrial Chemicals Co.
Organometallics— Catalysts for Isotactic Polymers F O R a long time, m a n has been fascinated with the precise order of nature. Now through the use of organometallic compounds like alumi 46 A
n u m alkyls with transition metals halides as catalysts, he is approaching nature's preciseness by building poly merized molecules—molecules hav ing an exceptional regularity of structure. And while this m a y seem like a significant breakthrough, it's only the beginning. Coordinated anionic catalysis has reached a remarkable state of development in a short time, but the study of the nature of the catalysts is at its very beginning. It's a complicated one, though. T h e action of a hetero geneous catalyst is dependent not only on the chemical action of the catalyst but also on the shape of the crystals, surface irregularities, and crystal lattice. While the pic ture is thus complicated, it is known that the activity of the best stereospecific catalyst in alpha-olefin poly merization is connected with a coor dinating action of strongly electro positive transition metal atoms, situ ated on the surface of a solid microcrystalline phase—for instance, lowvalence halides—which promotes the chemisorption of metallorganics. M a n y halides of polyvalent metals (also some halides corresponding to the highest valence of the same transition metals which in their lower valence state are employed now in anionic catalysis) m a y act as FriedelCrafts catalysts. T h e electropositivity of a transition metal atom in creases as its valence decreases. T h e most interesting catalysts, the ones which are highly stereospecific in the polymerization of alpha-olefins, act only in a heterogeneous phase. While it's a difficult j o b to establish the true chemical nature of the active centers of the catalysts, d a t a are now available which indicate the catalytic action is connected with the existence of metallorganic com plexes, mostly electron-deficient mol ecules, in which the carbon atom, in order to be coordinated with the central strongly electropositive metals, must be rich in electrons and therefore must derive from an anionic form, which m a y be origi nated by the polarization of the olcfinic double bond. Heterogeneous Catalysts
T h e first catalysts described by Ziegler and most widely studied are those obtained by reaction of TiCl 4 with Al-trialkyls. T h e reac tion, which is complex, takes place in several stages. T h e first step
INDUSTRIAL AND ENGINEERING CHEMISTRY
of titanium alkylation is followed by a successive stage of homolytic decomposition of the titanium trichloromonoalkyl compound. D u r ing this stage free radicals are formed and at the same time a reduction of titanium from valence 4 to 3 or less takes place. In general, when alkylaluminum compounds react with a titanium tetrahalide, a precipitate is obtained whose composition varies according to the A l / T i ratio, the temperature, the time, and the kind of alkyl group used. As a consequence, this precipitate ex hibits a catalytic action which varies with its composition and with time, but is in some cases very high. Such a precipitate contains those elements combined with each other in complexes whose formation is due to the character of a Lewis acid of the Al-trialkyl. T h e aluminum alkyl compounds can't be separated from the di- and trivalent titanium halides, even by washing with inert solvents. T h e fact that the primary process in the reaction of T1CI4 with A1R 3 is an alkylation, leading to the formation of an alkylated titanium compound (which decomposes, yield ing free radicals) induced m a n y chemists to think that the T1CI4AIR3 system could act as the initiator of a free radical type polymerization and that monomeric units, absorbed in ordered succession on the surface of a solid phase, could add to each other, thus forming sterically or dered structures. T h e formation of free radicals, which is observed during the formation of the catalyst, can in fact start the polymerization of certain monomers—e.g., styrene, diolefins—but not that of aliphatic α-olefins to high polymers, when the process is carried out at low tem perature and low pressure, in the presence of solvents. In studying the α-olefin polymerization, Natta was able to get certain highly stereospecific catalysts, yielding substan tially only isotactic polymers and others yielding only atactic poly mers. Professor N a t t a achieved in teresting results in producing iso tactic polymers by means of catalysts which show a high stability with time. T h e y were obtained by con tact of insoluble crystalline halides (with layer lattices) of di- or trivalent transition metals with organometallic compounds. Such catalysts may, if suitable metal-organic compounds are used (ΑΙ-triethyl, Be-diethyl, etc.) be highly stereospecific and yield
EgggCTggffg^gEEngTqgrg isotactic, highly crystalline polymers. O n the contrary, by means of the same organometallic compounds a b sorbed on amorphous carriers con taining transition metals compounds, amorphous atactic polymers are obtained. Coordinated Anionic Catalysis
T h e mechanism responsible for making isotactic molecules m a y be ascribed to the particular coordina tion bonds contained in the catalysts used in the reaction. Arguments in favor of the hypothesis of a co ordinated anionic catalysis are the following : 1. The nature of the terminal groups contained in the macromolecules, char acterized by the presence of terminal vinylidenic groups at one end of the chain, and, at the other end, of terminal alkyl groups corresponding to the normal saturated alkyl containing the same number of carbon atoms as the poly merized normal olefins. 2. The presence in the most active catalysts of different metals which are all highly electropositive. 3. The stronger catalytic activity of the complexes containing metallic ions which generate locally more intense electric fields and have a small atomic radius: beryllium (ionic radius 0.35 Α.), aluminum (0.51 Α.), and lithium (0.7 Α.). The most stereospecific catalysts are those in which the carbanion is co ordinated to a metal cation having a very small diameter—e.g., Al, Be, Li. The highest stereospecificity is observed with alkyl beryllium compounds. 4. The different reactivity of the monomers in the catalysis, which follows a reverse order in respect to that of the cationic catalysis. 5. The nature of chain termination reactions, which leads to the formation of a vinylidene bond through transfer of a hydrogen atom from the CHR group. 6. Lack of ability of certain solvents— e.g., cumene, iso-octane—known for their ability to pick up free radicals, to lower the molecular weight, unlike what happens in free radical polymeriza tion. 7. Constant ratio of polymerization with time, observed when stabilized catalysts are used. The solid catalyst is not consumed, unlike all the free radical initiators. Practical Developments
Among the unlimited n u m b e r of isotactic polymers obtainable from various vinyl monomers, practical interest will concentrate on those whose monomers are already widely available (polypropylene, polybutene, polystyrene) and which can
be synthesized at low cost. I n Italy, possible applications of iso tactic polymers have been studied for a considerable time. T h e first commercial product, polypropylene, m a d e possible by organometallics, will be commercially available from Montecatini before the end of this year. T h e product will be manufac tured and marketed by Montecatini under the trade n a m e M O P L E N . A more detailed treatment of the characteristics of stereospecific cataly sis, by N a t t a , given at the September 1958 International Meeting on Chem istry of Coordination Compounds, will be published in a special issue of Ricerca Scientifica by the National Re search Council, Rome, Italy. M A R I O L.
problem is not so serious as in the Wurtz reaction. O n l y a small per centage of the organotins of com mercial significance are tetraalkyl or tetraaryl. T h e compounds of highest importance are products prepared from tin containing two or three carbon-tin bonds. Before these derivatives can be prepared, a halide must be attached to the tin. Usually chlorine or bromine is used, attached by redistribution or cleav age: R4Sn + SnCU — 2 R2SnCl2 2RH + R2SnCl2 R4Sn + 2HC1 Most commercial processes are based on redistribution in the in terest of economy. Although it is possible to prepare all the mono-, di-, and trihalides by this method, the procedure varies considerably.
OTTOLENGHI
Chemore Corp.
Organotin Compounds
Vinyltin Compounds
O F THE several commercial proc esses for preparing organotin com pounds, the magnesium or Grignard reaction is the most flexible. T h e process is similar to the Wurtz process, with the organotins being formed stepwise : RMgCl + SnCb -* RSnCb + MgCl2 RMgCl + RSnCb — «R2SnCl2 + MgCb RMgCl + R2SnCh — R3SnCl + MgCl2 RMgCl + RsSnCl -* R4Sn + MgCl2
Vinyltin compounds are relatively new and appear to have m a n y inter esting physical and chemical proper ties. Seyferth prepared tetravinyltin from vinyl magnesium bromide and stannic chloride. He then employed the Kocheshkov method of redistribu tion to obtain vinyltin chlorides which were used as intermediates. Recently Rosenberg, Gibbons, and Ramsden reported the preparation of vinyltin compounds from vinyl mag nesium chloride. Their methods:
Although some side reactions oc cur with the Grignard reaction, the
These Are the O r g a n o t i n Compounds You Can Buy Tetraalkyl/ Aryltins
Trialkyl/ Aryltins
Tetrabutyltin Tetraphenyltin
Triphenyltin chloride Tributyltin chloride Triphenylhydroxide Tributyltin o x i d e Triphenyltin X Tributyltin X
Now
Dialkyltins Dibutyltin Dibutyltin Dibutyltin Dibutyltin Dibutyltin Dibutyltin Dibutyltin
sulfide dichloride oxide maleate dilaurate mercaptans X2
A v a i l a b l e in Ton Quantities on Special Order Tetralauryltin Dibutyldiphenyltin Dibutyldilauryltin Tetravinyltin Tetraoctyltin Dibutyltin R'2 Dimethyldibutyltin
Triphenyltin oxide Trivinyltin X Trioctyltin X Monoalkyltins
Divinyltin dichloride Dioctyltin dichloride Diphenyltin dichloride Dimethyltin dichloride R2SnX2
Butyltin trichloride Butyltin X3
Stannanes Hexabutylstannane
R' = a l k y l / a r y l group X = electronegative group
VOL. 49, NO. 12
·
DECEMBER 1957
47 A
Washing and Flotation Separation Cassiterite
S,
SnO, As
Sb
Cu
As
Sb
Fe
Calciner Granite
HCI Anthracite Silica-Lime Leaching
Filter
•^•^Ι^Π Electrolysis Chlorine
SnCI,
Still Chlorination Unit SnCI,
Commercial Uses of Organotin Compounds
SnCI.
Reactor
Equilibration
Still
Distillate
Hydrolizer
Filter
Drier Centrifuge
Packaging
Pulverizer
Packaging
Organotins—from ore to finished product To obtain the metal, the ore is first pulverized and washed to remove granite or state. Sulfides and arsenides of lead, antimony, copper, and iron are removed by flotation. The concentrate is calcined, and some sulfur, arsenic, and antimony are removed by volatilization. A hot hydrochloric acid leaching removes remaining metallic impurities. The residue, consisting mostly of tin dioxide, is mixed with anthracite and reduced in a gas- or oil-fired reverberatory furnace. Silica or limestone is used as a flux. Tin is then tapped from the bottom of the furnace. An alternative method is to convert the oxide to sodium stannate and recover the tin electrolytically. Chlorine is passed through the tin to yield stannic chloride. The product is purified by distillation and added to a Grignard reagent appropriate for the organotin compound to be manufactured. This process usually yields a tetraalkyl or aryltin which is purified by distillation. After this, the product reacts with stannic chloride to yield the desired product of redistribution, dependent on reactant ratios. Distillation is again used for purification, after which final derivatives are prepared by hydrolysis. Dependent upon the physical form, the product is finally filtered or centrifuged and dried prior to packaging for sales
4CH2=CHMgCl + SnCl4-«-(CH2=CH)1g
2
2CH 2 =CHMgCI + (C,H9)2SnCl2 _ (C4H9)2Sn(CH:=CH2)2 + 2MgCl3 CH2=CHMga + (C6H*)3SnCl (C 6 H 5 ) 3 SnCH=CH 2 + MgGls 48 A
-*
During the research it was discovered that vinylalkyltins could also be Prepared from alkyltin oxides: 2CH 2 =CHMgCl + (C
