metal-organic compounds - ACS Publications

A

New

Method

for

the

Synthesis

of Tetraethyllead

T. H. PEARSON, S. M. BLITZER, D. R. CARLEY, T. W. McKAY R. L. RAY, L. L. SIMS, and J. R. ZIETZ

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 9, 2016 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0023.ch028

Ethyl Corp., Baton Rouge, La.

It was discovered that successful reactions could be obtained between a wide variety of organometallic compounds and lead sulfide, lead oxide, and the lead salts of inorganic or organic oxy- and thioacids. Even mixed compounds of lead oxide and the lead salts of the organic oxyacids undergo reaction to form tetraethyllead. In particular, organometallic compounds of elements in Groups ΙΑ, IIA, IIIA, and IIB as well as the complex organometallic compounds derived from the elements in these groups, such as lithium tetraethylaluminum, are effective in reactions with nonhalide lead compounds of these types. Tetraorganolead yields vary with reaction conditions, reactants, and solvents used. Temperature condi tions required to initiate reactions are mild and in some cases are as low as —24°C. Rates of reaction are moderate to rapid, depending on the reaction conditions. Solvents are desirable to improve either reaction control and/or contact between reactants when one or both are solids under normal conditions. Solvents which have been used successfully in these reactions include hydrocarbons, amines, ethers, es ters, and chlorinated hydrocarbons. It is the aim of this paper to cite a number of examples, so that the reader can appreciate the broad scope of the reac tion of organometallic compounds with nonhalide lead compounds.

In recent years Ethyl Corp.'s research chemists have discovered a number of interest ing new reactions in their exploration of new methods of synthesizing organolead com pounds and, in particular, tetraethyllead Another paper (15) describes several of these methods in which the ethylating agents are ethyl esters of inorganic or organic acids and the lead-containing reactants are alloys of lead or lead metal itself. This paper describes some other methods in which the ethylating agents are organometallic compounds and the lead containing reactants are lead sulfide, lead oxides, or lead salts of inorganic or organic oxy- and thioacids. Presented here is a brief account of some of the research work done in this field to date. Because of time limitations, many of the details are omitted and the exam299

METAL-ORGANIC COMPOUNDS Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

300

ADVANCES IN CHEMISTRY SERIES

pies are r e s t r i c t e d t o the p r e p a r a t i o n of t e t r a e t h y l l e a d . I t i s i n t e n d e d t o p u b l i s h , a t some f u t u r e d a t e , a d d i t i o n a l p a p e r s w h i c h w i l l t r e a t i n greater d e t a i l e a c h o f t h e m a j o r phases o f t h e w o r k h e r e i n d e s c r i b e d .


Historical T h e first successful s y n t h e s i s of t e t r a e t h y l l e a d i s g e n e r a l l y a s c r i b e d t o L o w i g (9) w h o , i n 1853, o b t a i n e d t h i s c o m p o u n d f r o m t h e r e a c t i o n o f e t h y l i o d i d e w i t h s o d i u m l e a d a l l o y s c o n t a i n i n g 16 t o 2 5 % s o d i u m . T h e present c o m m e r c i a l m e t h o d f o r t e t r a e t h y l l e a d m a n u f a c t u r e i s a m o d i f i c a t i o n of Lowig's d i s c o v e r y as d e s c r i b e d i n a p a t e n t issued t o K r a u s a n d C a l l i s ( 7 ) i n 1926. C l o s e l y f o l l o w i n g Lowig's w o r k was t h a t o f B u c k t o n (1) w h o , i n 1859, r e p o r t e d t h e synthesis o f t e t r a e t h y l l e a d b y r e a c t i o n o f d i e t h y l z i n c a n d l e a d c h l o r i d e . T h i s i s t h e first e x a m p l e o f t h e p r e p a r a t i o n o f t e t r a e t h y l l e a d b y r e a c t i o n of a n o r g a n o m e t a l l i c c o m p o u n d w i t h a l e a d s a l t . Since t h a t t i m e , a n u m b e r o f p u b l i c a t i o n s h a v e a p p e a r e d d e a l i n g w i t h t h e s y n t h e s i s o f t e t r a o r g a n o l e a d c o m p o u n d s b y reactions analogous t o that w h i c h B u c k t o n discovered. T h e s e a r e s u m m a r i z e d b y Jones a n d G i l m a n (6) a n d L e e p e r , S u m m e r s , a n d G i l m a n (8) a n d f o r t h a t reason are o m i t t e d here. How ever, w i t h one e x c e p t i o n , t h e l e a d salts used w e r e a l l h a l i d e s . T h e one e x c e p t i o n i s r e p o r t e d b y N a d a n d K o c h e s h k o v (11) o n t h e f o r m a t i o n of d i a r y l l e a d acetates b y reactions of d i a r y l m e r c u r y c o m p o u n d s w i t h l e a d acetate i n c h l o r o f o r m s o l u t i o n . T h e p r o d u c t s o f these reactions are o n l y p a r t i a l l y a r y l a t e d , h o w e v e r , a n d s t i l l r e t a i n s a l t l i k e properties. T h u s , t h e l i t e r a t u r e c o n t a i n s n o reference t o t h e f o r m a t i o n o f t e t r a o r g a n o lead compounds b y reaction of a n organometallic c o m p o u n d w i t h lead compounds o t h e r t h a n l e a d halides. A c o n s i d e r a b l e a r e a of i g n o r a n c e has e x i s t e d r e g a r d i n g the p o t e n t i a l r e a c t i v i t y of m a n y other lead compounds t o w a r d organometallic compounds i n t h e synthesis of tetraorganolead products. E t h y l C o r p . ' s c h e m i s t s e x p l o r e d t h e field o f l e a d c o m p o u n d s e x p e r i m e n t a l l y , so as t o i n c l u d e (1) l e a d sulfide, (2) t h e oxides of l e a d , (3) the l e a d salts o f i n o r g a n i c a n d o r g a n i c t h i o - a n d o x y a c i d s , a n d (4) t h e m i x e d c o m p o u n d s of l e a d oxide w i t h t h e l e a d salts of o r g a n i c o x y a c i d s .

Reactions of Organometallic

Compounds with Sulfide and Oxides of Lead

P r o b a b l y t h e m o s t s i g n i f i c a n t d i s c o v e r y discussed i n t h i s p a p e r i s t h a t l e a d s u l fide, l e a d oxide, a n d l e a d d i o x i d e react w i t h o r g a n o m e t a l l i c c o m p o u n d s t o f o r m t e t r a e t h y l l e a d . F o r t h e m o s t p a r t , t h e o r g a n o m e t a l l i c c o m p o u n d s a r e d e r i v e d f r o m ele ments i n G r o u p s I A , H A , I I I A , and I I B of the periodic table. C o n s i d e r i n g the i n e r t ness o f these l e a d c o m p o u n d s , i t was s o m e w h a t s u r p r i s i n g t o find t h a t t h e y p a r t i c i p a t e d i n these r e a c t i o n s . E v e n m o r e u n e x p e c t e d was t h e fact t h a t t h e p r i m a r y o r g a n o l e a d p r o d u c t o f these reactions was c o m p l e t e l y e t h y l a t e d .

Table I.

Mole Ratio EtM«/PbS 4.9

EtM° C H Li 2

Tetraethyllead Yields from Reactions with Lead Sulfide

6

C2H5L1 + C H N a C H MgBr (C H5)2Mg

1.1 3.4 1.0

(C H ) Zn NaZn(C H )3

4.0 3.0

(C H ) A1 LiAl(C H )4 NaAl(C H )4

3.1 1.0 3.3

2

2

5

6

2

2

6

2

6

2

2

6

3

6

2

2

6

Reaction Conditions

E t M Concn., Moles/L.

Time, hr.

Temp., °C.

Yield, % *

0.43 0.10 0.87

2.5 4.5 3.5

35 25 110

15 81 6

0.15 7.7

3.0 3.5

35 110

42 53

0.97 0.37 0.09 0.70

9.0 1.5 4.2 1.0

-24 110 120·= 110

30 65 38 66

a

Solvent Diethyl ether Toluene Diethyl ether Toluene Dimethyl ether Toluene Hexane Toluene

° E t M = organometallic compound. & Based on 50% » theoretical conversion of lead in sulfide to (C H )4Pb. (C H*)4Pb + 2Li S + Pb. « Reaction conducted under pressure. 2

2

5

Example: 4 C H L i + 2PbS ->

2


2

6

PEARSON ET AL—SYNTHESIS OF TETRAETHYLLEAD

301


S h o w n i n T a b l e I a r e some e x a m p l e s o f results o b t a i n e d i n r e a c t i o n s o f t y p i c a l o r g a n o m e t a l l i c c o m p o u n d s d e r i v e d f r o m elements i n G r o u p s Ι Α , Π Α , Π Ι Α , a n d I I B w i t h lead sulfide. B o t h t h e simple a n d complex organometallic compounds react w i t h l e a d sulfide t o f o r m t e t r a e t h y l l e a d . T h e h i g h e s t y i e l d c i t e d ( 8 1 % ) is f o r t h e r e a c t i o n o f a m i x t u r e o f e t h y l l i t h i u m a n d e t h y l s o d i u m [ p r e p a r e d a c c o r d i n g t o W i t t i g ' s m e t h o d f o r s o d i u m d i p h e n y l l i t h i u m (17)] w i t h l e a d sulfide i n d i e t h y l e t h e r u s i n g a n o r g a n o m e t a l l i c - l e a d sulfide m o l e r a t i o o f 1 t o 1. T h i s e x a m p l e i s i n s t r u c t i v e i n s h o w i n g t h e m i l d c o n d i t i o n s u n d e r w h i c h these reactions proceed. T h e 8 1 % y i e l d was o b t a i n e d i n 4.5 h o u r s a t 2 5 ° C . Possibly more s t r i k i n g p r o o f o f t h e ease w i t h w h i c h these r e a c t i o n s p r o c e e d i s t h e e x a m p l e o f z i n c t r i e t h y l s o d i u m w h i c h gave a 3 0 % y i e l d i n r e a c t i o n w i t h l e a d sulfide a t — 2 4 ° C . i n 9 hours. T h e other examples presented show the v a r i e t y of organometallic compounds w h i c h react w i t h l e a d sulfide t o f o r m t e t r a e t h y l l e a d . M o d e r a t e l y h i g h y i e l d s were o b t a i n e d for t h e conditions used w i t h sodium t e t r a e t h y l a l u m i n u m ( 6 6 % ) , t r i e t h y l a l u m i n u m ( 6 5 % ) , a n d d i e t h y l z i n c ( 5 3 % ) . L o w e r y i e l d s were o b t a i n e d w i t h t h e o t h e r o r g a n o metallic compounds under the reaction conditions cited. I n T a b l e I I are presented similar data f o r reactions of organometallic

Table II. Oxide of Lead PbO

Tetraethyllead Yields from Reactions with Oxides of Lead

6

C H MgBr (C H ) Mg

2.4 2.0

(C H ) Zn (C H ) A1 LiAl(C H )4 NaAl(C H ) (C H ) A1

0.5 0.7 1.8 0.5 1.3

2

6

2

6

2

2

6

2

2

6

3

2

Pb0

Mole Ratio EtM°/Oxide 3.0

EtM« C H Li 2

6

2

2

2

6

3

6

4

Reaction Conditions

E t M Concn., Mole/L.

Time, hr.

Temp., °C.

Yield, % »

0.19 0.28

3.0 3.0

125' 120

64 13

0.15 0.19 0.70 0.16 0.70 —

6.0 4.5 2.5 2.0 1.0 2.0

35 110 110 130* 110 105

18 47 63 64 3 19*

a

Solvent Diethyl ether Hexane Diethyl ether Toluene Hexane Toluene None

° E t M = organometallic compound. Based on 50% theoretical conversion of lead to (C He)4Pb. Conducted under pressure. Based on 100% theoretical conversion of lead in P b 0 to i C H ) P b . 2A1 0 . b

compounds

c

2

c

d

2

2

2

6

4

3Pb0 + 4(C H ) Al -> 3(C H ) Pb + 2

2

fi

3

2

6

4

3

w i t h l e a d oxide a n d a single r e a c t i o n o f t r i e t h y l a l u m i n u m w i t h l e a d d i o x i d e . With the exception of t h e reaction of d i e t h y l m a g n e s i u m a n d lead oxide, a l l t h e other reac t i o n s were c a r r i e d o u t a b o v e 1 0 0 ° C . i n t h e e x a m p l e s p r e s e n t e d . R e a s o n a b l y h i g h y i e l d s were o b t a i n e d w i t h l i t h i u m t e t r a e t h y l a l u m i n u m ( 6 4 % ) , e t h y l l i t h i u m ( 6 4 % ) , a n d t r i e t h y l a l u m i n u m ( 6 3 % ) . D i e t h y l z i n c gave a moderately h i g h y i e l d ( 4 7 % ) a n d smaller y i e l d s were o b t a i n e d w i t h t h e o t h e r o r g a n o m e t a l l i c c o m p o u n d s . T h e e x a m p l e of t h e r e a c t i o n of l e a d d i o x i d e w i t h t r i e t h y l a l u m i n u m s h o w n i n T a b l e I I w a s c a r r i e d o u t i n t h e absence of s o l v e n t . A y i e l d o f 1 9 % t e t r a e t h y l l e a d w a s o b t a i n e d i n 2 h o u r s a t a t e m p e r a t u r e of 1 0 5 ° C . O r g a n o m e t a l l i c c o m p o u n d s w h i c h a r e n o r m a l l y l i q u i d s , s u c h as t r i e t h y l a l u m i n u m o r d i e t h y l z i n c , m a y b e r e a c t e d i n t h e absence of s o l v e n t w i t h l e a d sulfide a n d t h e l e a d oxides. H o w e v e r , some care m u s t b e exercised u n d e r these c o n d i t i o n s t o a v o i d r a p i d heat g e n e r a t i o n a n d e v e n v i o l e n t r e a c t i o n . T h e use o f s o l v e n t s p e r m i t s b e t t e r r e a c t i o n c o n t r o l t h r o u g h i m p r o v e d heat r e m o v a l a n d a g i t a t i o n . W h e n t h e o r g a n o m e t a l l i c c o m p o u n d s a r e n o r m a l l y solids, s o l v e n t s a r e d e s i r a b l e f o r t h e reasons s t a t e d a b o v e a n d also t o s o l u b i l i z e t h e r e a c t a n t s , t o p e r m i t m o r e r a p i d r e a c t i o n t h r o u g h i m p r o v e d contact.

Reaction of Lead Salts of Inorganic Acids A n u m b e r o f r e a c t a n t c o m b i n a t i o n s o f o r g a n o m e t a l l i c c o m p o u n d s a n d l e a d salts of i n o r g a n i c o x y - a n d t h i o a c i d s were also f o u n d t o p r o d u c e t e t r a o r g a n o l e a d c o m p o u n d s .



302

F o r p u r p o s e s o f b r e v i t y , h o w e v e r , t h e r e a c t i o n s of o n l y t h r e e l e a d salts w i t h t r i e t h y l a l u m i n u m are presented t o illustrate t h e results obtained.

Table III.

Lead Salt PbS0 Pb(N0 )

Mole Ratio EtsAlVSalt 1.4 0.61

4

8

2

Pb(SCN)


1 b

Tetraethyllead Yields from Reactions of Triethylaluminum with Lead Salts of Inorganic Acids

2

0.66

Solvent Toluene Ethylene glycol dimethyl ether Toluene

Et»Al« Concn., Mole/L. 0.7 0.9 0.5

Reaction Conditions Time.hr. 1 1 3

Temp., °C. 110 85 110

Yield,* % 54 50 39

EtsAl = triethylaluminum. Based on 50% theoretical conversion of lead to tetraethyllead.

A s s h o w n i n T a b l e I I I , l e a d s u l f a t e a n d n i t r a t e gave 54 a n d 5 0 % y i e l d s , r e s p e c t i v e l y , under t h e conditions tested. L e a d thiocyanate reacted t o give a 3 9 % y i e l d of t e t r a e t h y l l e a d . S i m i l a r results were o b t a i n e d w i t h o t h e r l e a d salts i n t h i s class, s u c h as l e a d borate and lead carbonate. F o r t h e e x a m p l e s s h o w n , toluene o r e t h y l e n e g l y c o l d i m e t h y l e t h e r s o l v e n t s were s a t i s f a c t o r y . R e a c t i o n t e m p e r a t u r e s a t a b o u t t h e b o i l i n g p o i n t of t h e s o l v e n t s w e r e adequate t o give the stated yields i n 1 t o 3 hours' reaction time. A r a t h e r s t r i k i n g c o l o r c h a n g e o c c u r s d u r i n g r e a c t i o n . T h e l e a d salts t e s t e d a r e w h i t e , b u t p r o m p t l y o n i n i t i a t i o n of t h e r e a c t i o n t h e s u r f a c e of t h e s a l t p a r t i c l e s t u r n s d a r k a n d t h e n b l a c k . T h i s is due t o t h e f o r m a t i o n of m e t a l l i c l e a d d u r i n g t h e r e a c t i o n w h i c h i s d e p o s i t e d o n t h e s u r f a c e of t h e salt p a r t i c l e s . I n m a n y cases, t h i s c h a n g e occurs almost instantaneously when the organometallic c o m p o u n d is brought into con t a c t w i t h t h e l e a d s a l t . T h i s o b s e r v a t i o n i l l u s t r a t e s t h e h i g h degree o f r e a c t i v i t y o f t h e o r g a n o m e t a l l i c c o m p o u n d s w i t h l e a d c o m p o u n d s of t h e t y p e discussed i n t h i s p a p e r .

Reactions with Lead Salts of Organic Acids A n u m b e r of l e a d salts of o r g a n i c a c i d s were t e s t e d w i t h v a r i o u s o r g a n o m e t a l l i c c o m p o u n d s , p a r t i c u l a r l y those of elements i n G r o u p s I A , I I A , I I I A , a n d I I B . I n a l l cases successful r e a c t i o n s w i t h t h e f o r m a t i o n of t e t r a o r g a n o l e a d c o m p o u n d s o c c u r r e d . R e a c t i o n s w i t h l e a d salts of t h i s t y p e are c h a r a c t e r i z e d b y r a p i d r e a c t i o n rates a n d h i g h y i e l d s . T h i s i s p a r t i c u l a r l y t r u e f o r those l e a d salts o r o r g a n i c acids w h i c h h a v e a moderate o r h i g h s o l u b i l i t y i n t h e solvents. C o m p l e t e l y homogeneous reactions are possible w i t h some l e a d salts a n d t h e o r g a n o m e t a l l i c c o m p o u n d s b y s e l e c t i o n o f t h e p r o p e r s o l v e n t s . U n d e r s u c h c o n d i t i o n s , m a x i m u m r e a c t i o n rates a r e p o s s i b l e . T h e p o t e n t i a l o f s u c h r e a c t i o n s w i l l b e m o r e e v i d e n t as specific e x a m p l e s are discussed. A n u m b e r of e x a m p l e s of r e a c t i o n s w i t h l e a d salts o f o r g a n i c a c i d s a r e p r e s e n t e d i n T a b l e s I V , V , a n d V I . I n T a b l e I V are s h o w n t w o e x a m p l e s w i t h l e a d f o r m a t e , t h e salt o f t h e s i m p l e s t o r g a n i c a c i d . F o r t h e e x a m p l e s s h o w n , d i e t h y l z i n c i n t o l u e n e r e a c t e d a l m o s t q u a n t i t a t i v e l y ( 9 5 % y i e l d ) b a s e d o n t h e a m o u n t of d i e t h y l z i n c u s e d , t o f o r m t e t r a e t h y l l e a d . T h e r e a c t i o n w a s c o n d u c t e d a t 1 1 1 ° C . f o r 1.5 h o u r s . T r i -

Table IV. EtM> (C H ) Zn (C H ) A1 2

6

2

2

6

3

a 6

Tetraethyllead Yields from Reactions with Lead Formate

Mole Ratio EtMVSalt 0.73 0.45

E t M Concn., Mole/L. 0.70

Reaction Conditions

a

Solvent Toluene Diethylene glycol dimethyl ether

0.70

Time, hr. 1.5 1.5

Temp., °C. Ill 100-110

E t M = organometallic compound. Based on 50% theoretical conversion of lead to tetraethyllead.


Yield,* % 95 73

PEARSON ET AL.—SYNTHESIS OF TETRAETHYLLEAD Table V.

Mole Ratio EtM«/Salt 1.67 0.91

(C H ) Zn (C H,) A1

1.0 0.61

2

6

2

3

6

2

0 b

Reaction Conditions

E t M " Concn., Mole/L. 1.0

Time, hr. 1.7

0.34 0.70

2 1

0.70 0.73 0.70

0.5 1.5 3

Temp., °C. 60 60-100 111 room temp. 66 111

Yield," % 100 76 93 97 96 73

E t M = organometallic compound. Based on 50% theoretical conversion of lead to tetraethyllead.

Table VI.

Lead Lead Lead Lead

Solvent Heptane Ethylene glycol dimethyl ether Toluene Diethylene glycol dimethyl ether Tetrahydrofuran Toluene

0.61 0.50

NaAl(C H )4


Tetraethyllead Yields from Reactions with Lead Acetate

EtM« (CtHs)Na (CaHOîMg

2

303

Lead Salt tetraacetate stéarate oxalate naphthenate**

Lead linoresinate*

Tetraethyllead Yields from Reaction of Triethylaluminum with Other Lead Salts of Organic Acids Mole Ratio Et Al«/Salt 1.0 0.71 0.66 0.54 3

1.0

Et3Al Concn., Mole/L. 0.35 0.35 0.49

Reaction Conditions

a

Solvent Toluene Ethylene glycol dimethyl ether

Time, hr. 2.5 0.5 3.0

0.70 0.70

0.25 1.0

Temp., ° C . 0-10 111 111

Yield, % 65 81" 18

room temp. 111

91 94

6

E t A l = triethylaluminum. Based on 100% theoretical conversion of lead to tetraethyllead. All others based on 50% theoretical conversion of lead to tetraethyllead. Naphthenic acid is a mixture of cycloparaffinic acids. « Derived from tall oil which contains resin and fatty acids.

0

3

6 e

d

e t h y l a l u m i n u m i n diethylene glycol d i m e t h y l ether gave a 7 3 % y i e l d under essentially t h e same c o n d i t i o n s o f r e a c t i o n t i m e a n d t e m p e r a t u r e . I n T a b l e V are shown other examples of reactions of organometallic compounds w i t h l e a d acetate, t h e s a l t o f a n o t h e r s i m p l e o r g a n i c a c i d . O u t s t a n d i n g i s t h e q u a n t i t a t i v e y i e l d o b t a i n e d w i t h e t h y l s o d i u m i n h e p t a n e . I n t h i s p a r t i c u l a r r e a c t i o n , excess e t h y l s o d i u m w a s u s e d t o g i v e t h e o r e t i c a l ( 5 0 % ) c o n v e r s i o n o f t h e l e a d i n l e a d acetate to t e t r a e t h y l l e a d . N e a r q u a n t i t a t i v e yields were obtained i n reactions of t r i e t h y l a l u m i n u m ( 9 7 % ) a n d d i e t h y l z i n c ( 9 4 % ) , r e s p e c t i v e l y , w i t h l e a d acetate. W i t h t r i e t h y l a l u m i n u m , t h e l e a d acetate w a s i n excess a n d w i t h d i e t h y l z i n c t h e r e a c t a n t s were p r e s e n t i n e q u i m o l a r ( t h e o r e t i c a l ) q u a n t i t i e s . I n b o t h o f these cases t h e r e a c t i o n t i m e s w e r e short. Striking is the 9 7 % y i e l d obtained w i t h t r i e t h y l a l u m i n u m i n y hour a t room t e m p e r a t u r e . T h i s i l l u s t r a t e s t h e fast r e a c t i o n rates a n d h i g h y i e l d s o b t a i n a b l e i n these a c t i o n s u n d e r v e r y m i l d c o n d i t i o n s . T h e o t h e r e x a m p l e s ( d i e t h y l m a g n e s i u m and sodium t e t r a e t h y l a l u m i n u m ) gave poorer yields u n d e r the conditions cited. I n T a b l e V I a r e s h o w n e x a m p l e s o f r e a c t i o n s o f t r i e t h y l a l u m i n u m w i t h l e a d salts of m o r e c o m p l e x o r g a n i c a c i d s i n c l u d i n g o x a l i c , s t e a r i c , n a p h t h e n i c a c i d s , a n d a c i d s d e r i v e d f r o m t a l l o i l . I n a d d i t i o n , a n e x a m p l e o f a q u a d r i v a l e n t l e a d salt i s ^;iven t o c o m p l e t e t h i s g e n e r a l class o f l e a d salts o f o r g a n i c a c i d s . L e a d t e t r a a c e t a t e , u s i n g a n excess o f t r i e t h y l a l u m i n u m , g a v e a 6 5 % y i e l d of t e t r a e t h y l l e a d a t 0 ° t o 1 0 ° C . i n 2.5 h o u r s ' r e a c t i o n t i m e . T h i s also r e p r e s e n t s a 6 5 % c o n version o f lead i n this salt t o tetraethyllead, w h i c h indicates t h a t t h e potential c o n v e r s i o n o f l e a d i n t h i s q u a d r i v a l e n t l e a d salt i s 1 0 0 % . T h e l e a d salts o f a c i d s d e r i v e d f r o m t a l l o i l , n a p h t h e n i c , a n d s t e a r i c a c i d s g a v e h i g h y i e l d s u n d e r t h e c o n d i t i o n s tested ( 9 4 , 9 1 , a n d 8 1 % , r e s p e c t i v e l y ) . T h e 9 1 % y i e l d obtained w i t h lead naphthenate i n % hour a n d t h e 8 1 % yield obtained w i t h lead stéarate i n y h o u r a g a i n i l l u s t r a t e t h e r a p i d r e a c t i o n rates possible. R e a c t i o n s s u c h as these a r e h o m o g e n e o u s , because t h e o r g a n o m e t a l l i c c o m p o u n d s a s w e l l a s t h e l e a d salt a r e s o l u b l e . I n t h e case o f l e a d n a p h t h e n a t e , w h i c h i s c o m p l e t e l y s o l u b l e i n t h e solvent, t h e r a p i d reaction a n d h i g h y i e l d were obtained a t r o o m t e m p e r a t u r e . 2

2



304

Reactions with Mixed Compounds of Lead Oxide and Lead Salts of Organic Acids L e a d oxide forms m i x e d compounds w i t h lead salts of organic acids. Because l e a d o x i d e a n d t h e l e a d salts i n d e p e n d e n t l y r e a c t w i t h o r g a n o m e t a l l i c c o m p o u n d s , i t w a s o f i n t e r e s t t o d e t e r m i n e w h e t h e r t h e m i x e d c o m p o u n d s w o u l d also r e a c t t o f o r m tetraethyllead. I n a l l cases t e s t e d , these m a t e r i a l s r e a c t e d t o f o r m t e t r a e t h y l l e a d . S o m e e x a m p l e s are s h o w n i n T a b l e V I I . L e a d f o r m a t e - l e a d o x i d e ( 1 t o 1 m o l e r a t i o ) g a v e a 5 0 %


Table VII.

Lead Salt Formate Acetate Stéarate

Tetraethyllead Yields from Reactions with Triethylaluminum with M i x e d Compounds of Lead O x i d e a n d Lead Salts of Organic Acids Mole Ratio PbO/Salt 1 to 1

Mole Ratio EteAlVMixed Compound 1.3

1 to 1 2 toi 5 to 1 1 to 1

1.3 1.9 4.0 1.2

3 to 1 5 to 1

2.2 3.1

Solvent Ethylene glycol dimethyl ether Toluene Ethylene glycol dimethyl ether

Et3Al° Concn., Mole/L.

Reaction Conditions Time, hr.

Temp., °C.

Yield,* %

0.70 0.70 0.30 0.30

1.5 1 3 3

85 85 111 111

50 70 38 25

0.70 0.70 0.35

1 1.5 3

85 85 85

80 55 53

° EteAl = triethylaluminum. Based on 50% theoretical conversion of lead to tetraethyllead. b

y i e l d . T h r e e m i x e d c o m p o u n d s of l e a d oxide a n d l e a d acetate were t e s t e d i n w h i c h t h e o x i d e - s a l t m o l e r a t i o s were 1 t o 1, 2 t o 1, a n d 5 t o 1. T h e y i e l d s decreased p r o g r e s s i v e l y f r o m 7 0 % t o 2 5 % as t h e r a t i o i n c r e a s e d . T h e same t r e n d w a s o b s e r v e d f o r t h e l e a d o x i d e - l e a d stéarate series t h o u g h t h e y i e l d d r o p c o r r e s p o n d i n g t o t h e h i g h e s t l e a d o x i d e - c o n t a i n i n g m i x e d c o m p o u n d w a s less severe t h a n f o r t h e acetate series. T h e s e a n d r e l a t e d d a t a suggest t h a t t h e m i x e d salts t e n d t o r e a c t as a m i x t u r e of the t w o components. F u r t h e r w o r k is necessary t o c l a r i f y these r e l a t i o n s h i p s .

Experimental M o s t r e a c t i o n s discussed i n t h i s p u b l i c a t i o n were c a r r i e d o u t i n glassware r e a c t o r s fitted w i t h a g i t a t o r , condenser, t h e r m o m e t e r , a n d s t o p p e r e d o p e n i n g s f o r t h e i n t r o d u c t i o n of reagents. I n g e n e r a l , t h e a n h y d r o u s l e a d c o m p o u n d a n d s o l v e n t were i n t r o d u c e d i n t o t h e r e a c t i o n flask w h i c h h a d b e e n p u r g e d w i t h d r y n i t r o g e n . A f t e r t h e r e a c t o r c o n t e n t s h a d been b r o u g h t t o t h e d e s i r e d r e a c t i o n t e m p e r a t u r e , t h e o r g a n o m e t a l l i c c o m p o u n d was a d d e d t o t h i s a n h y d r o u s e n v i r o n m e n t . W h e n t h e s t a t e d r e a c t i o n period w a s ended, t h e mass w a s allowed t o cool a n d t h e residual organometallic c o m p o u n d destroyed w i t h i s o p r o p y l alcohol a n d water. T h e organic layer was t h e n analyzed for tetraethyllead. T h e v a r i o u s o r g a n o m e t a l l i c c o m p o u n d s u s e d i n t h i s w o r k were p r e p a r e d b y r e l i a b l e p r o c e d u r e s r e p o r t e d i n t h e l i t e r a t u r e . T h e G r i g n a r d reagents (12) were u s e d i n e t h y l e t h e r s o l u t i o n as p r e p a r e d . T h i s w a s also t r u e of t h e e t h y l l i t h i u m u s e d (3). Tri e t h y l a l u m i n u m a n d i t s d e r i v a t i v e s were p r e p a r e d ether-free b y r e p o r t e d p r o c e d u r e s (4) · D i e t h y l m a g n e s i u m was p r e p a r e d f r o m t h e G r i g n a r d reagent ( b r o m i d e ) b y t h e d i o x a n e p r e c i p i t a t i o n m e t h o d (H). D i e t h y l z i n c w a s s y n t h e s i z e d f r o m e t h y l i o d i d e a n d zinc m e t a l p o w d e r b y t h e u s u a l p r o c e d u r e (10). E t h y l s o d i u m w a s s y n t h e s i z e d f r o m d i e t h y l m e r c u r y a n d s o d i u m (13). R e a g e n t g r a d e l e a d c o m p o u n d s were u s e d i n a l l cases. T h e s e m a t e r i a l s w e r e v a c u u m dried o r dried b y azeotropic distillation. L e a d naphthenate was obtained f r o m A d v a n c e S o l v e n t s C o . a n d t h e l e a d s a l t of t a l l o i l f r o m t h e H a r s h a w C h e m i c a l C o . R e a g e n t g r a d e o r h i g h g r a d e c o m m e r c i a l s o l v e n t s were u s e d , d e p e n d i n g o n a v a i l a b i l i t y . T h e s e m a t e r i a l s were d r i e d o v e r s o d i u m w i r e a n d u s e d w i t h o u t f u r t h e r p u r i f i cation.


305

PEARSON ET AL—SYNTHESIS OF TETRAETHYLLEAD

Two different analytical methods were used to determine the tetraethyllead formed. The dithizone method (16) was used when low yields were obtained; for sub stantial yields, the iodometric (δ) method was employed. In many cases, the tetra ethyllead was isolated from the reaction mass by vacuum distillation and identified by its physical properties. Yields were calculated, for all reactions cited in this paper, on the basis of the valency of the lead compound used. It was assumed that the maximum possible conversion of lead in the divalent compound was 50% as given by the example: 4C H Li + 2PbO -* (C H ) Pb + Pb + 2Li 0


2

5

2

5

4

2

This is consistent with the known stoichiometry of the reaction with the divalent halides (2). In the case of lead dioxide and lead tetraacetate, the yield was based on the assumption that the maximum possible conversion of lead in these quadrivalent compounds was 100%. Literature Cited (1) Buckton, G., Ann. 109, 218 (1859). (2) Frankland, E., Lowrance, Α., J. Chem. Soc. 35, 245 (1879). (3) Gilman, H., Beel, J. Α., Branner, C. G., Bullock, M . W., Dunn, G. E., Miller, L. S., J. Am. Chem. Soc. 72, 1689 (1950). (4) Grosse, Α. V., Mavity, J. M., J. Org. Chem. 5, 106 (1940). (5) Hein, F., Klein, Α., Mesee, H . J., Z. anal. Chem. 115, 177-33 (1939). (6) Jones, R. G., Gilman, H., Chem. Revs. 54, 835 (1954). (7) Kraus, C. Α., Callis, C. C . (to Standard Oil Development Co.), U . S. Patent 1,612,131 (Dec. 28, 1926). (8) Leeper, R. W., Summers, L., Gilman, H., Chem. Revs. 54, 101 (1954). (9) Löwig, C., J. prakt. Chem. 60, 304 (1853). (10) Meyer, M . , Chem. News 131, 1 (1925). (11) Nad, M . M . , Kocheshkov, Κ. Α., J. Gen. Chem. (U.S.S.R.) 12, 409 (1943). (12) Org. Syntheses, Coll. Vol. 1, 306 (1941). (13) Schlenk, W , Holtz, J., Ber. deut. chem. Ges. 50, 262 (1917). (14) Schlenk, W., Schlenk, W., Jr., Ibid.,62, 920 (1929). (15) Shapiro, Hymin, ADVANCES IN C H E M . SER., No. 23, 290 (1958). (16) Snyder, L. J., Ind. Eng. Chem, Anal. Ed. 19, 684 (1947). (17) Wittig, G., Ludwig, R., Polster, R., Chem. Ber. 88, 294 (1955). RECEIVED for review May 10, 1957. Accepted June 1, 1957.


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