A S T A F F F E A T U R E
A LOOK A T LITHIUM COMPOUNDS Increased use of stereospecgc polymerization catalysts focuses attention on lithium and its compounds metal, in contrast to other alkali metals, is Lithium relatively inert, but the reactivity of its compounds is unique. And this reactivity can be the key to a whole host of new chemicals, new compounds, new reactions. This does not imply that lithium chemicals have not been known or used to any great extent in the past. Quite the contrary. Many have proved useful in many applications and still do today. I n today’s changing technology, with changing needs, lithium chemicals and compounds will be once again in demand, although lithium has for a while slipped from a place of prominence and given way to less exotic compounds and less expensive combinations. And the demand will stem not from any single pressure but from the characteristics of the new lithium chemicals about to make their commercial debut. In his early work, Ziegler found butyllithium attractive in promoting his now famous reactions. But it is said he switched to aluminum alkyls in the belief that the price of lithium would prevent widespread use of the catalyst. So, lithium catalysts, acknowledged for their potency, lost the first round on a competitive price count, not technological feasibility. There is reason to believe that the price advantage of aluminum alkyls over butyllithium may be slipping away and processing advantages of the butyllithium may outweigh any slight price disadvantage. As the field of polymer chemistry becomes more complex and reactions more involved, the need for a “directing” catalyst may become more pronounced and the use of butyllithium increased. inorganic Chemicals
Progress in lithium chemistry has kept pace with the advances in chemistry in general. For example, developments in lithium chemistry have been consistent with the preparation of new, diverse, and powerful reducing agents containing unusual anions. Lithium nitride may possess the capability to complement alumi50
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
num hydride and borohydrides and their substituted derivates in many organic reactions. P. E. Koenig and coworkers at Coates Chemical Laboratories, LSU, briefly discussed their observations on the reactions of organic substrates with ionic nitrides, specifically lithium nitride, in the November 1961 issue of the Journal o f Organic Chemistry. They concluded that the ionic nitrides constitute a class of reagents of wide applicability and are currently looking at a variety of addition reactions, displacements, and polymerization as well as use of dispersions and fused-salt solutions of the nitrides in organic reactions. Lithium nitride is insoluble in most conventional organic media. I t is sparingly soluble in polyethers (dial)-me for example). Such organic work as is being done involves such solvents. Lithium nitride is formed, in part, when finely divided lithium metal is exposed to moist air under controlled conditions. Recent work at Foote Mineral has shown that up to 50 weight per cent lithium nitride may accumulate in lithium metal dispersions exposed to air at room temperature and 50 per cent relative humidity. However, the existence of the nitride under these conditions is transitory since the nitride is subsequently hydrolyzed by atmospheric moisture to produce ammonia gas and lithium hydroxide. The ultimate corrosion product of lithium metal exposed to ambient air is lithium carbonate. A study of the interaction of lithium metal with air and its component gases has been reviewed favorably for publication in the Journal of Chemical Engineering Data. Lithium nitride may find application as a nitriding agent in metallurgical processes, as a reducing and nucleophilic reagent in organic reactions, such as noted above, and in certain inorganic reactions where the presence of the unusual trivalent nitride group is of interest. Lithium hydride is another of the family of lithium chemicals evolving from the lithium-nitrogen-hydrogen system. It finds application in organic synthesis, as a raw material for production of lithium amide, lithium aluminum hydride, lithium borohydride, and other complex hydrides. I t serves as a chemical reducing agent, catalyst, lightweight hydrogen source (it contains about 12.5 weight per cent hydrogen), and in nuclear shielding. Inhibition of the thermal decomposition of lithium perchlorate is made possible by the addition of certain silver salts. As the proportion of the silver salt is in-
AN HYDROUS
When anhydrous ammonia is passed over lithium wire at ambient temperature, a reaction between the ammonia and lithium takes place. Foote Mineral's Research
and
Development
Group,
Exton, Pa., gave a dramatic demonstra-
ANHYDROUS
of
tion
lithium
this into
evidence
technique ammonia
is
the
for
getting
solution.
First
of
blue
formation
streaks on the wire, followed by the formation
of rust to russet colored
droplets.
As the reaction proceeds
there is sometimes a temperature rise, but the solubility o f lithium does not in-
As the droplets increase in size, they run off the wire and can be collected. This material
crease appreciably.
is
a
yellow-gold,
characteristic
of
concentrated solutions o f alkali metals in
liquid ammonia.
The
lithium-am-
monia solution i s thought t o have the lowest density of any known solution-
C.
about 0.46 at 19'
About 1 1 cc.
of solution were formed in 1 hour and 15 minutes. been
increased by using a
extractor. in
Reaction rate could have The solution
ammonia
is
Soxhlet
of lithium metal
regarded
by
Foote
scientists as a member o f the series of materials available from the ternary combination of elements, lithium, nitrogen, and hydrogen.
The distinct and
characterized compounds, lithium amide, imide, nitride, azide, and hydride all stem
from
this
Each compound, ammonia
family
of
elements.
as well as lithium-
solution,
possesses
unique
properties of interest to both organic and inorganic chemists. VOL. 5 4
NO. 6 J U N E 1 9 6 2
51
creased the rate of decomposition is stabilized. AM.arkowitz and Boryta, Foote Mineral Co., reported in the February 1962 issue of the Journal of Physical Chemistry that stabilization was evident in a mixture of 85 mole yo lithium perchlorate to which had been added 15 mole silver nitrate. The mixture was stabilized for 39 to 45 hours at 417.8’ C. The work is significant in that lithium perchlorate has been suggested as a rocket propellant oxidizer. A discussion of the solubility trends of lithium perchlorate appeared in the July 1961 issue of the Journal of Chemical Engineering Data. The solubility and stability of the perchlorate has prompted its use in studies of salt effects in organic reactions. Lithium metaphosphate and pyrophosphate are suggested as possible components for fused salt nuclear breeder blankets (Journal of Inorganic & Aiuclear Chem. 22, 293-6, 1961). The metaphosphate is expressed simply as L i p 0 3 but like other water-insoluble alkali metal metaphosphates it is undoubtedly a salt of highly polymeric, long-chain structure. Its value as a breeder blanket lies in the relatively high thermal stability and low absorption of thermal neutron characteristic of phosphorus compounds. Recent studies at Foote Mineral suggest that no polyphosphate higher than the pyrophosphate has been found to exist within the liquid region of the lithium metaphosphate-lithium pyrophosphate system. EDITOR’S NOTE
The reader w i l l j n d in lhis month’s companion quarterly, I H E C Product Research and Development, 1, N o . 2, a number of articles dealing with current work in the fields of polymerization, hydrogenation, and isomerization. Specijic efect of the presence of lithium compounds on the course of reactions is reported in two articles: “Catalytic Hydrogenation of Nitrosamines to c‘nsymmetrical Hydrazines and A ATew Hydrocarbon Elastomer. ” A n indication of future trends in processing ethylenepropylene polymers and in polymerization of isoprene will be found in: “Properties of an Ethylene-Propylene-n’onconjugated Diene Terpolymer” and “Ethylene-Propylene Vulcanization with Aralkyl Peroxides and Coagents.” The efect of certain metals and metal oxides is given in: “Skeletal Isomerization of Olejins over Aluminum Fluoride Catalysts.” Further evidence of the reactivity of lithium compounds and its combinations was given in a report on the formation of stereoblock copolymers before the Division of Polymer Chemistry at the 141st ACS National Meeting. A highly dispersed heterogeneous catalyst mixture in T i e l 4 with lithium-aluminum alkyl was used in the pieparation of these copolymers. True copolymers, made only by the block polymerization technique, are a coming reality now lhat the catalyst has been found to do the job. 52
INDUSTRIAL AND ENGINEERING C H E M I S T R Y
Organic Chemicals
Butyllithium has made its mark in polymerization reactions. Its facility and high reactivity have led to further research into the butyllithium family. T h e result is a series of compounds which offer wide possible range of applications. The high solvation energy of lithium ions allows great control over the nature of lithium organics. But solvent environment is not responsible for the differences in reactivity of the various butyllithiums listed in the following table. These differences are caused by the location of the lithium on the molecule. A change in solvent from a hydrocarbon to an ether, such as tetrahydrofuran, increases reactivity of all of these compounds. I n polymerization it greatly increases the speed of initiation and polynierization hut at the cost of losing lithium’s stereospecific properties. Comparative Activity
4
3 2 I
Butyllithium Compound
Normal Is0 Secondary Tertiary
Comparative .A uailability
1 4 2
3
Uses for all four are the same. Choice depends on reactivity desired or required; availability, stability, and cost. n-Butyllithium is usually chosen because it is most readily available, most stable on storage, and cheapest even though it is slightly less reactive than the other butyllithiums. One of the most interesting of the new lithium organic compounds is monolithium acetylide. Currently the acetylide is used in making vitamin A and steroids. Its present manufacture requires formation and reaction of the acetylide in liquid ammonia at -33” C. A new technique has been developed where the acetylide can be made at room temperature in a variety of organic solvents. I t has been stabilized and can be stored at room temperature. Monolithium acetylide can be used in any reaction where the ethynyl group is needed. I t can bc used to replace sodium acetylide where sodium gives low yields. Apparently the lithium form has a low steric requirement permitting greater directional activity. Several other lithium organics of note are about to make their commercial appearance : Phenyllithium
lsopropyllithium Methyllithium lithium methoxide
suggested for introducing phenyl group where phenyl Grignard yields are l o w o r t o metalate an organic compound Comparable in reactivity t o tertbutyllithium For hindered steroid positioning A strong base, suggested for ester exchange reactions
Low equivalent weight of lithium, 6.94, makes for compounds of high anion content. High solvation energy gives compounds of unusual solubility characteristics. It is in the combination of these properties that the future of lithium compounds lie.
