Preparation and Ignition Properties of Aluminum Alkyls - Advances in

Preparation and Ignition Properties of Aluminum Alkyls

METAL-ORGANIC COMPOUNDS Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 06/09/15. For personal use only.

CHARLES J. MARSEL, EMIL O. KALIL, ANTHONY REIDLINGER, and LEONARD KRAMER Department of Chemical Engineering, New York University, New York, Ν. Y., and Wright Aeronautical Division, Curtiss-Wright Corp., Woodridge, N. J.

Three years ago, a joint project was established by the Wright Aeronautical Division, Curtiss-Wright Corp., at the Jet and Flame Laboratory of New York University, to study the preparation and behavior of pyrophoric organometallic compounds. The aluminum alkyls have been one of the most interesting groups studied to date, from an ignition standpoint. Compounds capable of ready spontaneous ignition with air are of considerable potential importance for certain types of air-breathing power plants. Certain thermal theories of flame propagation suggest that the flame is propagated by virtue of continuous spontaneous ignition occurring on the leading edge of the flame front; in such a case, the time lapse before the flame appears—ignition delay—would be an important factor. Although aluminum alkyls have been known for some time, it has been only during the past few years that these compounds have been the subject of extensive research, largely because of the use of these compounds by Ziegler as catalysts for olefin polymerizations at low pressures. Preparation of Aluminum Alkyls A c o n v e n i e n t m e t h o d f o r t h e p r e p a r a t i o n of s m a l l q u a n t i t i e s of these c o m p o u n d s i n v o l v e s a d i s p l a c e m e n t r e a c t i o n b e t w e e n a l u m i n u m m e t a l a n d t h e a l k y l c o m p o u n d of some less a c t i v e m e t a l ( w h i c h c a n be r e a d i l y p r e p a r e d ) — e . g . , t h e r e a c t i o n of d i m e t h y l m e r c u r y w i t h a n excess of a l u m i n u m y i e l d s t r i m e t h y l a l u m i n u m a n d m e r c u r y (2) : 2A1 + 3 ( C H ) H g — 2 ( C H ) A 1 + 3 H g 3

2

3

3

A l t h o u g h t h i s p r o c e d u r e gives g o o d y i e l d s f o r l o w e r m e m b e r s of t h e series, t h e decreased s t a b i l i t y of t h e h i g h e r m e r c u r y a l k y l s l i m i t s i t s usefulness. T h e cost of s u c h a m e t h o d w o u l d be h i g h . R e c e n t l y Z i e g l e r h a s d e v e l o p e d s e v e r a l n e w m e t h o d s of p r e p a r i n g a l u m i n u m a l k y l s u s i n g olefins as t h e s t a r t i n g reagents (10, 11). A t a b o u t 100° C . l i t h i u m a l u m i n u m h y d r i d e reacts w i t h e t h y l e n e a n d t e t r a e t h y l a l u m i n u m l i t h i u m is f o r m e d : LiAlH

4

+ 4C H 2

4

-> L i A l ( C H ) 2

5

4

W h e n t h i s q u a t e r n a r y salt is t r e a t e d w i t h a l u m i n u m c h l o r i d e , t r i e t h y l a l u m i n u m is formed : 3LiAl(C H ) 2

5

4

+ AICI3 - * 3LÎC1 + 4 A 1 ( C H ) 2

5

3

T h i s m e t h o d has b e e n used t o p r e p a r e t h e c o r r e s p o n d i n g η - p r o p y l a n d n - h e x y l c o m pounds. A m o r e e c o n o m i c a l process f o r t h e l a r g e scale p r o d u c t i o n of these c o m p o u n d s i n v o l v e s s p r a y i n g a l u m i n u m i n t o a n a t m o s p h e r e of h y d r o g e n a n d a n olefin (12):

172

MARS EL, KALIL, REIDLINGER, AND KRAMER—ALUMINUM ALKYLS

173

A l + 3 C H + 3 / 2 H -> A1(C H ) 2

4

2

CH3

Al + 3 C H = C 2

2

+ 3/2H -* |

/

2

\

\ CH3

5

3

/CH3

^CH—CH

2

)A1

/

\CH3


A l k y l a l u m i n u m h y d r i d e s m a y be f o r m e d b y a d j u s t i n g t h e p r o p o r t i o n s o f t h e r e a c t a n t s : 2R A1 + A1 + 3 / 2 H -> 3R A1H 3

2

2

I t i s e v i d e n t t h a t t r i m e t h y l a l u m i n u m , t h e s i m p l e s t m e m b e r o f t h e series, a n d t h e one w h i c h i s o f m o s t i n t e r e s t i n t h i s s t u d y , c a n n o t b e m a d e b y t h e r e a c t i o n s w h i c h i n v o l v e t h e use o f olefins as s t a r t i n g m a t e r i a l s . T o p r e p a r e t h i s c o m p o u n d one c a n e m p l o y t h e g e n e r a l r e a c t i o n o f a n a l k y l h a l i d e a n d a l u m i n u m , w h i c h results i n t h e f o r m a t i o n o f a n e q u i m o l a r m i x t u r e of the m o n o a l k y l a l u m i n u m d i h a l i d e a n d d i a l k y l a l u m i n u m monohalide called a sesquihalide : 2A1 + 3 R X -> RoAlX + R A 1 X 2

I n g e n e r a l , t h e sesquiiodides r e a d i l y d i s p r o p o r t i o n a t e o n h e a t i n g , a n d t r i m e t h y l a l u m i n u m m a y be p r e p a r e d b y h e a t i n g m e t h y l a l u m i n u m sesquiiodide a n d r e m o v i n g t h e m o s t v o l a t i l e c o m p o n e n t , t r i m e t h y l a l u m i n u m , f r o m t h e t o p of a f r a c t i o n a t i n g c o l u m n (8). T h i s c o n v e n i e n t m e t h o d for p r e p a r i n g t r i m e t h y l a l u m i n u m w a s i n i t i a l l y u s e d i n these l a b o r a t o r i e s for the p r e p a r a t i o n of p o u n d q u a n t i t i e s of t h i s c o m p o u n d . Preparation of T r i m e t h y l a l u m i n u m from M e t h y l Iodide and A l u m i n u m . Tri m e t h y l a l u m i n u m , t r i e t h y l a l u m i n u m , a n d some of t h e i r h a l i d e s are e x t r e m e l y r e a c t i v e substances w h i c h a r e s p o n t a n e o u s l y f l a m m a b l e i n a i r a n d r e a c t w i t h w a t e r w i t h explosive violence. C a r e m u s t b e t a k e n t h a t a l l a p p a r a t u s i s c o m p l e t e l y d r y before s t a r t i n g a n y e x p e r i m e n t s . I t i s also i m p o r t a n t t h a t a p p a r a t u s b e selected i n w h i c h t h e r e i s l i t t l e p o s s i b i l i t y f o r t h e d e v e l o p m e n t of a i r l e a k s . B y f a r t h e m o s t a n n o y i n g d i f f i c u l t y e n c o u n t e r e d i n these l a b o r a t o r i e s was t h e d e v e l o p m e n t of a i r l e a k s d u r i n g t h e f r a c t i o n a t i o n s t e p , because a l u m i n u m o x i d e c a n d e p o s i t i n t h e c o l u m n a n d i t m a y become plugged. A l u m i n u m t u r n i n g s ( 4 p o u n d s ) a r e p l a c e d i n a 1 2 - l i t e r glass flask a t t a c h e d t o t h e b o t t o m o f a n efficient f r a c t i o n a t i n g c o l u m n . M e t h y l i o d i d e ( 2 p o u n d s ) i s i n t r o d u c e d , a n d the m i x t u r e is r e f l u x e d b y e x t e r n a l h e a t i n g u n t i l t h e r e a c t i o n becomes s p o n t a n e o u s , as e v i d e n c e d b y a s u d d e n increase i n t e m p e r a t u r e i n t h e r e a c t i o n flask a n d b y blackening of the a l u m i n u m surface. ( T h e initiation of this reaction m a y be hastened b y a d d i n g a s m a l l a m o u n t o f the p r o d u c t o b t a i n e d f r o m a p r e v i o u s r e a c t i o n o r b y t h e addition of iodine o r of a l u m i n u m chloride.) T h e remainder of the m e t h y l iodide (23 p o u n d s ) is t h e n a d d e d a t a r a t e sufficient t o m a i n t a i n a p o t t e m p e r a t u r e of a b o u t 160° F . , w i t h e x t e r n a l heat b e i n g r e q u i r e d o n l y o c c a s i o n a l l y i n the l a t e stages o f t h e r e a c t i o n . T h i s r e a c t i o n i s s l o w a n d a d d i t i o n t i m e s o f 2 4 t o 4 8 h o u r s were n o t u n common. W h e n t h e r e a c t i o n i s c o m p l e t e , the m i x t u r e i s d i s t i l l e d t h r o u g h a 6-foot c o l u m n p a c k e d w i t h p r o t r u d e d stainless steel p a c k i n g . T h e reflux r a t i o is a d j u s t e d t o m a i n t a i n a h e a d t e m p e r a t u r e b e l o w 72° C . a t 100 m m . of m e r c u r y p r e s s u r e , a n d v a r i e s f r o m 4 t o 1 a t t h e b e g i n n i n g o f t h e d i s t i l l a t i o n t o a b o u t 19 t o 1 a t the e n d o f t h e d i s t i l l a t i o n . T h e t r i m e t h y l a l u m i n u m i s a colorless l i q u i d , b o i l i n g a t 69° t o 72° C . a t 100 m m . a n d is o b t a i n e d i n y i e l d s o f 50 t o 6 5 % o f t h e o r y ( a b o u t 2.5 p o u n d s ) . T w o o b v i o u s d i s a d v a n t a g e s o f the a b o v e p r o c e d u r e are the cost o f the s t a r t i n g reagent m e t h y l i o d i d e , a n d t h e r e l a t i v e l y l o n g t i m e r e q u i r e d f o r the slow d i s t i l l a t i o n a n d e q u i l i b r a t i o n w h i c h i s necessary i n o r d e r t o o b t a i n a p u r e p r o d u c t . A n obvious i m p r o v e m e n t over this procedure w o u l d involve the substitution of m e t h y l c h l o r i d e f o r the m o r e e x p e n s i v e m e t h y l i o d i d e . M e t h y l a l u m i n u m s e s q u i c h l o r i d e c a n r e a d i l y be p r e p a r e d f r o m m e t h y l c h l o r i d e a n d a l u m i n u m f o i l , w h i c h a l l o w s a l a r g e s u r f a c e a r e a f o r a g i v e n w e i g h t of m e t a l .

ADVANCES IN CHEMISTRY SERIES

174


Preparation of M e t h y l a l u m i n u m Sesquichloride. I n a d r y 2-liter, three-necked flask fitted w i t h a condenser, m e r c u r y - s e a l s t i r r e r , i n l e t f o r gases, a n d t h e r m o m e t e r , are p l a c e d 3 2 0 g r a m s of a l u m i n u m f o i l ( h o u s e h o l d g r a d e ) , w h i c h h a s been c u t i n t o s m a l l pieces. T h e t h e r m o m e t e r s h o u l d e x t e n d 2 o r 3 i n c h e s i n t o t h e flask, i n o r d e r t o measure the v a p o r temperatures over the reacting mass. A schematic d i a g r a m of t h e a p p a r a t u s i s p r e s e n t e d i n F i g u r e 1. A c r y s t a l o f i o d i n e i s p l a c e d i n t h e flask, w h i c h i s

methyl chloride

water-cooled condenser

semi-ball joints

mercury bubbler Figure

mercury bubbler

1. Apparatus for preparation of aluminum alkyls

t h e n flushed w i t h m e t h y l c h l o r i d e . T o i n i t i a t e t h e r e a c t i o n , 5 o r 6 m l . o f m e t h y l i o d i d e a r e i n t r o d u c e d i n t o t h e flask t h r o u g h t h e condenser. T h e flask i s t h e n h e a t e d u n t i l t h e r e a c t i o n s t a r t s , a n d a s u d d e n rise i n t e m p e r a t u r e t o 1 5 0 ° C . i s n o t e d . T h e source of h e a t i s r e m o v e d , a n d t h e r e a c t i o n c o n t i n u e s u n t i l t h e m e t h y l i o d i d e i s c o n s u m e d ; this takes about % hour. T h e a d d i t i o n of m e t h y l chloride is begun a n d continued a t a rate w h i c h maintains a pressure, w i t h i n t h e system, equal t o o r slightly greater t h a n atmospheric pressure. M e r c u r y bubblers before a n d after t h e system w i l l give a q u a l i t a t i v e m e a s u r e o f t h e r a t e o f passage o f m e t h y l c h l o r i d e i n t o a n d o u t of t h e r e a c t i o n flask. T h e r e a c t i o n i s s u s t a i n e d b y i t s o w n h e a t , a n d t h e t e m p e r a t u r e s h o u l d be k e p t b e t w e e n 9 0 ° a n d 120° C . T h e a d d i t i o n o f m e t h y l c h l o r i d e i s s t o p p e d w h e n its a b s o r p t i o n n o l o n g e r o c c u r s a t a reasonable r a t e — t h i s r e q u i r e s a b o u t 20 h o u r s . T h e mass i s n o w e n t i r e l y l i q u i d , a n d n o a l u m i n u m m e t a l r e m a i n s . T h e y i e l d of m e t h y l a l u m i n u m sesquichloride is q u a n t i t a t i v e (based o n a l u m i n u m ) . ( N o t e . T h e a b o v e p r o c e d u r e h a s also b e e n u s e d i n these l a b o r a t o r i e s f o r t h e p r e p a r a t i o n of e t h y l a l u m i n u m sesquichloride.) T h i s p r o d u c t ( m e t h y l a l u m i n u m s e s q u i c h l o r i d e ) does n o t r e a d i l y d i s p r o p o r t i o n a t e , a n d t r i m e t h y l a l u m i n u m c a n n o t b e o b t a i n e d as i n t h e case o f t h e s e s q u i i o d i d e . There are s e v e r a l a l t e r n a t i v e routes f o r t h e c o n v e r s i o n o f t h e s e s q u i c h l o r i d e t o t r i m e t h y l a l u m i n u m . These include:

175

MARSEL, KALIL, REIDLINGER, AND KRAMER-ALUMINUM ALKYLS

R e d u c t i o n of the s e s q u i c h l o r i d e w i t h s o d i u m m e t a l . Separation of d i m e t h y l a l u m i n u m chloride from m e t h y l a l u m i n u m dichloride through the f o r m a t i o n o f the n o n v o l a t i l e c o m p l e x C H A 1 C 1 · N a C l w i t h t h e s u b s e q u e n t r e d u c t i o n of d i m e t h y l a l u m i n u m c h l o r i d e w i t h s o d i u m . C o n v e r s i o n o f the s e s q u i c h l o r i d e t o d i m e t h y l a l u m i n u m c h l o r i d e b y the a d d i t i o n o f one m o l e of t r i m e t h y l a l u m i n u m t o o n e m o l e of t h e s e s q u i c h l o r i d e , a n d subsequent r e d u c t i o n w i t h s o d i u m of t h e d i m e t h y l a l u m i n u m c h l o r i d e . 3

2


R e d u c t i o n o f the s e s q u i c h l o r i d e w i t h m e t a l l i c s o d i u m a p p e a r s t o o c c u r a c c o r d i n g t o t h e f o l l o w i n g e q u a t i o n (δ) : 3Na + MeAlCl

2

+ M e A l C l -> M e A l + A l + 3 N a C l 2

3

3

I n practice, the reaction is somewhat sluggish, a n d i t appears t h a t the f o r m a t i o n of a c o m p l e x b e t w e e n s o d i u m c h l o r i d e a n d m e t h y l a l u m i n u m d i c h l o r i d e causes some decrease i n yields. T h e fact that m e t h y l a l u m i n u m dichloride forms a nonvolatile complex w i t h s o d i u m c h l o r i d e , w h i l e d i m e t h y l a l u m i n u m c h l o r i d e does n o t , is u s e d as t h e basis f o r t h e f o l l o w ing separation. Separation of D i m e t h y l a l u m i n u m Chloride from M e t h y l a l u m i n u m D i c h l o r i d e . T o t h e s e s q u i c h l o r i d e o b t a i n e d f r o m 320 g r a m s of a l u m i n u m are a d d e d 450 g r a m s o f d r y s o d i u m c h l o r i d e , a n d the mass i s s t i r r e d a n d a l l o w e d t o reflux ( e x t e r n a l h e a t i n g i f n e c e s s a r y ) f o r 2 h o u r s . T h e flask i s a l l o w e d t o cool, a n d t h e a p p a r a t u s i s a r r a n g e d for distillation. T h e p r o d u c t , d i m e t h y l a l u m i n u m chloride, distills a t 126-7° C . a t a t m o s p h e r i c p r e s s u r e , a n d weighs 4 6 0 g r a m s ( 8 3 % o f t h e t h e o r e t i c a l b a s e d o n aluminum). D i m e t h y l a l u m i n u m c h l o r i d e c a n b e c o n v e r t e d t o t r i m e t h y l a l u m i n u m b y a single distillation w i t h sodium. Preparation of T r i m e t h y l a l u m i n u m from D i m e t h y l a l u m i n u m C h l o r i d e . T o a 5 0 0 - m l . , t h r e e - n e c k e d flask f i t t e d w i t h a r e f l u x c o n d e n s e r a n d a m e r c u r y seal s t i r r e r , are a d d e d 27 g r a m s o f s o d i u m . T h e a p p a r a t u s i s flushed w i t h n i t r o g e n a n d 100 g r a m s of d i m e t h y l a l u m i n u m c h l o r i d e are p u m p e d i n t o t h e flask. T h e m i x t u r e is g e n t l y h e a t e d w i t h slow s t i r r i n g u n t i l t h e r e a c t i o n s t a r t s ; t h i s o c c u r s w h e n t h e v a p o r t e m p e r a t u r e range i s 95° t o 100° C . T h e r e a c t i o n i s e x o t h e r m i c , a n d care m u s t b e t a k e n t o k e e p the r e a c t i o n u n d e r c o n t r o l . I f the r e a c t i o n becomes t o o v i g o r o u s , s t i r r i n g s h o u l d b e s t o p p e d a n d t h e flask c o o l e d . T h e m i x t u r e i s a l l o w e d t o reflux f o r 5 h o u r s . T h e c h l o r i d e - f r e e p r o d u c t w h i c h d i s t i l l s a t 127° t o 130° C . weighs 4 5 g r a m s ( 9 0 % o f theory). T r i e t h y l a l u m i n u m h a s also b e e n p r e p a r e d i n g o o d y i e l d s b y t h e a b o v e p r o c e d u r e . T h e t h i r d a l t e r n a t i v e process has n o t been i n v e s t i g a t e d i n these l a b o r a t o r i e s , b u t s h o u l d offer c o n s i d e r a b l e m e r i t f o r t h e large-scale p r o d u c t i o n o f t r i m e t h y l a l u m i n u m . I t has been r e p o r t e d t h a t t h e a d d i t i o n o f t r i e t h y l a l u m i n u m t o e t h y l a l u m i n u m s e s q u i c h l o r i d e results i n t h e f o r m a t i o n o f d i e t h y l a l u m i n u m c h l o r i d e (5). ( C H ) A 1 C 1 + C2H5AICI2 + ( C H ) A 1 - » 3 ( C H ) A 1 C 1 2

5

2

2

5

3

2

5

2

I f s u c h a r e a c t i o n o c c u r s w i t h t h e m e t h y l c o m p o u n d s , i t w o u l d offer a r e a s o n a b l e m e t h o d f o r the p r e p a r a t i o n of d i m e t h y l a l u m i n u m chloride, w h i c h could easily be c o n verted to trimethylaluminum. I n t h e N e w Y o r k U n i v e r s i t y laboratories d i m e t h y l a l u m i n u m chloride h a s been produced b y the reaction of m e t h y l chloride w i t h a n alloy of a l u m i n u m a n d magnesium. T h i s is a n extension of the w o r k of Grosse a n d M a v i t y (5) who p r e p a r e d d i e t h y l a l u m i n u m bromide f r o m e t h y l bromide a n d M a g n a l i u m , a n alloy consisting of 7 0 % a l u m i n u m a n d 3 0 % magnesium. W h e n m e t h y l chloride is allowed t o react w i t h a n alloy consisting of 7 0 % a l u m i n u m and 3 0 % magnesium, d i m e t h y l a l u m i n u m chloride


176 and magnesium chloride are formed. b y a one-step synthesis.

T h u s , d i m e t h y l a l u m i n u m chloride can be formed

4 C H C 1 + A l M g -> 2 ( C H ) A 1 C 1 + M g C l 3

2

3

2

2

Preparation of D i m e t h y l a l u m i n u m C h l o r i d e . T h e a p p a r a t u s i s s i m i l a r t o t h a t u s e d f o r t h e p r e p a r a t i o n of m e t h y l a l u m i n u m s e s q u i c h l o r i d e . T u r n i n g s of A l M g (60 g r a m s ) are p l a c e d i n a 5 0 0 - m l . , t h r e e - n e c k e d flask. ( A t t h e t i m e o f t h i s w o r k , t h i s a l l o y c o u l d n o t b e o b t a i n e d f r o m a c o m m e r c i a l source. I t was p r e p a r e d b y t h e D e p a r t m e n t of M e t a l l u r g i c a l E n g i n e e r i n g of N e w Y o r k U n i v e r s i t y . ) A s m a l l a m o u n t o f m e t h y l i o d i d e is i n t r o d u c e d , i n o r d e r t o s t a r t t h e r e a c t i o n , w h i c h i s t h e n a l l o w e d t o c o n t i n u e t h r o u g h t h e a d d i t i o n of m e t h y l c h l o r i d e . T h e r e a c t i o n m a s s s l o w l y changes f r o m a s o l i d t o a g r a y sludge as t h e r e a c t i o n p r o c e e d s . T h i s r e a c t i o n i s slower t h a n t h e one u s i n g p u r e a l u m i n u m , a n d u s u a l l y r e q u i r e s e x t e r n a l h e a t i n g t o m a i n t a i n a t e m p e r a t u r e i n t h e r a n g e o f 9 0 ° t o 120° C ; t h e r e a c t i o n is c o m p l e t e i n a b o u t 3 0 h o u r s . D i s t i l l a t i o n a t a t m o s p h e r i c p r e s s u r e y i e l d s 113 grams ( 8 0 % ) of d i m e t h y l a l u m i n u m chloride boiling a t 126-27° C . T h e t i m e required f o r t h e r e a c t i o n t o go t o c o m p l e t i o n increases a p p r e c i a b l y as t h e b a t c h size i s i n c r e a s e d . P r e p a r a t i o n of d i m e t h y l a l u m i n u m c h l o r i d e b y t h i s p r o c e d u r e is slow, a n d r e q u i r e s the use o f a n a l l o y w h i c h , w h e n a v a i l a b l e , i s s o m e w h a t m o r e e x p e n s i v e t h a n p u r e a l u m i n u m . F o r these reasons i t a p p e a r s t h a t t h e m e t h o d s w h i c h u t i l i z e t h e s e s q u i c h l o r i d e as a n i n t e r m e d i a t e a r e m o r e a t t r a c t i v e f o r t h e large-scale p r o d u c t i o n o f t r i methylaluminum . F o r t h e sake o f c o n v e n i e n c e t h e p h y s i c a l c o n s t a n t s o f t h e m e t h y l a n d e t h y l a l u m i n u m alkyls a n d chloro intermediates are summarized i n T a b l e I .


2

Physical Constants of Methyl a n d Ethyl Aluminum Alkyls and Their Chloro Intermediates

Table I. Compound

Boiling Point, °C.

Aluminum chloride, A l C h Methyl aluminum dichloride, CH3AICI2 Dimethyl aluminum chloride, (CH ) A1C1 8

2

Trimethyl aluminum, (CH ) A1 Ethyl aluminum dichloride, C2H5AICI2 Diethyl aluminum chloride, (C H )2A1C1 3

3

2

5

Triethyl aluminum, (C H )3A1 2

6

Melting Point, °C.

182.7 at 752 mm., sublimes at 177.8 (Handbook of Chemistry and Physics) 97-101 at 100 mm. (4) 83-4 at 200 mm. (4) 70-6 at 100 mm. (4) 58-60 at 20 mm. 125-6 at 755 mm. (4) 114.5-15.5 at 50 mm. (4) 125-6 at 50 mm. (4) 105-7 at 20 mm. 128-30 at 50 mm.

ά £, G . / C c . 2

194 at 5.2 mm.

2.44

72.7 (4) Below - 5 0

1.00

15 32 (4) Below - 5 0

0.752

Below - 1 8 -19.8

0.837

Where no reference is listed, values were determined in this laboratory.

Thermal Stabilities of Aluminum

Alkyls

T o measure t h e t h e r m a l stabilities of t r i m e t h y l a l u m i n u m a n d t r i e t h y l a l u m i n u m , t w o series of tests were c o n d u c t e d . I n t h e first series, a 1 0 3 - m l . stainless steel c y l i n d e r c o n n e c t e d t o a p r e s s u r e gage a n d v a l v e s y s t e m f o r i n t r o d u c i n g a n i t r o g e n a t m o s p h e r e w a s u s e d as a c o n s t a n t v o l u m e c o n t a i n e r . A b o u t 1 g r a m of s a m p l e was i n t r o d u c e d i n t o t h e c y l i n d e r i n a s c a l e d glass v i a l ; t h e cylinder was t h e n evacuated a n d filled w i t h nitrogen t o a pressure of 300 p.s.i.a. T h e v i a l w a s b r o k e n b y s h a k i n g t h e c y l i n d e r , a n d t h e c y l i n d e r w a s p l a c e d i n a h e a t i n g b a t h a t t h e d e s i r e d t e m p e r a t u r e . T e m p e r a t u r e a n d pressure r e a d i n g s were t a k e n a t definite t i m e i n t e r v a l s , a n d finally t h e pressure o f t h e s y s t e m , a f t e r c o o l i n g t o room temperature, was recorded. T h e results of these tests a r e s u m m a r i z e d i n T a b l e II.

Table II.

Thermal Stabilities of Trimethylaluminum and Triethylaluminum

Compound Al(CHs)3 Al(CH3)s

Conditions 300° F. for 2 hours 450° F . for 6 hours

A1(C2H6)3

300° F . for 2 hours

Results No evident decomposition 25 p.s.i. pressure increase; about 30% decomposition; pyrophoric residue No evident decomposition

177



T h e p r o c e d u r e i n v o l v e d i n t h e second series of tests w a s t h e same as t h a t d e s c r i b e d a b o v e , b u t i n t h i s case t h e v i a l s were n o t b r o k e n ( F i g u r e 2 ) . T u b e Β is a

A

Β

Figure 2. Thermal stability of trimethyl aluminum C a r i u s c o m b u s t i o n t u b e t h a t c o n t a i n e d a 1-ml. s a m p l e o f t r i m e t h y l a l u m i n u m w h i c h was h e a t e d a t 450° F . f o r 4 h o u r s . A y e l l o w s o l i d w a s f o r m e d ; t h e s o l i d w a s s h o w n t o be a l u m i n u m c a r b i d e . T u b e A is a s i m i l a r c o m b u s t i o n t u b e t h a t c o n t a i n e d a 1-ml. s a m p l e o f t r i e t h y l a l u m i n u m w h i c h was s u b j e c t e d t o s i m i l a r c o n d i t i o n s . I n t h i s case n o liquid remained, and i t appears that the solid contained metallic a l u m i n u m .

Compatibilities with Materials of

Construction

D u r i n g t h i s i n v e s t i g a t i o n , a n u m b e r o f tests were m a d e t o a s c e r t a i n w h e t h e r t h e a l u m i n u m a l k y l s a r e c o m p a t i b l e w i t h c e r t a i n m a t e r i a l s of c o n s t r u c t i o n . I n g e n e r a l , m o s t of t h e tests were m a d e a t r o o m t e m p e r a t u r e , b u t i n c e r t a i n cases tests were r u n a t e l e v a t e d t e m p e r a t u r e s . T h e tests i n v o l v e d i m m e r s i n g s a m p l e s o f t h e m a t e r i a l s i n t r i m e t h y l a l u m i n u m f o r v a r y i n g p e r i o d s of t i m e , a f t e r w h i c h t h e t r i m e t h y l a l u m i n u m w as r e m o v e d f r o m t h e test flask; t h e s a m p l e s were w a s h e d s e v e r a l t i m e s w i t h benzene a n d / o r carbon tetrachloride, removed, examined, a n d compared w i t h t h e original m a t e r i a l . T h e r e s u l t s of m a n y of these tests a r e s u m m a r i z e d i n T a b l e s I I I a n d I V . r

F r o m t h e d a t a l i s t e d i n T a b l e s I I I a n d I V i t is e v i d e n t t h a t a l u m i n u m , c o p p e r , a n d c a r b o n steel are n o t affected b y c o n t a c t w i t h t r i m e t h y l a l u m i n u m a t r o o m t e m p e r a t u r e , a n d i t h a s been o b s e r v e d t h a t s i l v e r s o l d e r , l e a d , b r a s s , a n d stainless steel d o n o t react t o a n y a p p r e c i a b l e e x t e n t . M o s t o f t h e r u b b e r s a n d t h e i r s u b s t i t u t e s r e a c t , t o some degree, w i t h t r i m e t h y l a l u m i n u m . T h i s is n o t surprising, f o r metal alkyls a r e v e r y reactive compounds w h i c h react w i t h u n s a t u r a t e d g r o u p s a n d g r o u p s w h i c h c o n t a i n a c t i v e h y d r o g e n s . I t is e x p e c t e d , t h e r e f o r e , t h a t t r i m e t h y l a l u m i n u m w o u l d r e a c t w i t h olefinic g r o u p s , c a r b o n y l g r o u p s , p r i m a r y a n d s e c o n d a r y a m i n o g r o u p s , a n d h y d r o x y l g r o u p s ; because t r i m e t h y l a l u m i n u m c a n b e c o n s i d e r e d t o b e a L e w i s a c i d , i t c a n c o m p l e x w i t h basic


178


Table III.

Effect of Immersing Certain Materials in Trimethylaluminum at Room Temperature

Material Cast iron Tungsten Molybdenum Zinc Aluminum Copper Carbon steel Celanese polyethylene U . S. Rubber polyacrylate, Style 9271 U. S. Rubber Paracril 18-80 Du Pont Neoprene G Ν Du Pont Neoprene W Enjay butyl rubber GR-1-18 Enjay butyl rubber GR-1-25 Enjay butyl rubber GR-1-35 Du Pont Hypalon magnesium oxide cure Du Pont Hypalon litharge cure Dow Corning Silastic 250 Du Pont Mylar Du Pont silicon rubbers U. S. Rubber 565 R U . S. Rubber 575 U. S. Rubber cured Neoprene 3077 U. S. Rubber 566R U. S. Rubber 3048 Kellogg Kel-F 3700 Kellogg Kel-F 5500-72 Du Pont Teflon

Table IV.

Exposure Period, Days 21 21 21 21 10 10 10 10 10 1 35 35 19 19 19 35 35 1 1 1 7 7 7 7 7 7 7 7

Condition after Exposure No apparent effect No apparent effect No apparent effect No apparent effect No apparent effect No apparent effect No apparent effect No apparent effect Surface hardened and cracked Loses elasticity, breaks easily Slight surface cracking, retains elasticity Tears easily, some loss of elasticity Very soft, spongy Very soft, spongy, blistered Swollen, very spongy Surface cracks, somewhat elastic Cracks on bending, slightly elastic Disintegrates Dissolves Disintegrates Blisters Hardens and blisters Blisters and hardens Hardens Hardens, cracks Unaffected except for slight discoloration Unchanged Unchanged

Effect of Immersing Certain Materials in Trimethylaluminum at Elevated Temperature

Material Kellogg Kel-F 5500-72 Kellogg Kel F NW-5 Kellogg Kel-F 5NW-25TR Kellogg Kel-F N - l Kellogg Kel-F compression-molded film Du Pont extruded black Teflon Du Pont Teflon sheet Du Pont Teflon sheet Du Pont Teflon sheet

Temperature, °F. 300-330 250-300 240-305 240-300 300 350 350 400 450

Time, Hours 1 2 1.5 1.5 1.5 1.5 1.5 1.5 1.5

Observation Reacts Sample dissolved Sample became porous Sample dissolved Reacts Sample recovered unchanged Sample recovered unchanged Sample recovered unchanged Sample recovered unchanged

c o m p o u n d s s u c h as ethers, t e r t i a r y a m i n e s , a n d sulfides. I n a d d i t i o n , t h e fillers o r p l a s t i c i z e r s c o u l d also r e a c t . T h e o n l y m a t e r i a l s w h i c h a r e c o m p a t i b l e w i t h t r i m e t h y l a l u m i n u m at room temperature are polyethylene, K e l - F , a n d Teflon. Because of i t s relatively l o w softening point, polyethylene cannot be used i n a n y applications at even moderate temperatures. A n u m b e r of K e l - F elastomers, compres s i o n - m o l d e d K e l - F f i l m , e x t r u d e d T e f l o n , a n d T e f l o n sheet were s u b j e c t e d t o i m m e r s i o n tests a t e l e v a t e d t e m p e r a t u r e s . A l l of t h e K e l - F m a t e r i a l s r e a c t e d t o some e x t e n t . T h i s m a y b e d u e t o t h e r e a c t i o n of t h e t r i m e t h y l a l u m i n u m w i t h t h e c h l o r i n e a t o m s i n t h e K e l - F p o l y m e r , o r t o t h e d e c o m p o s i t i o n of t h e K e l - F b y t h e loss o f c h l o r i n e a n d subsequent reaction w i t h the t r i m e t h y l a l u m i n u m .

Ignition Properties of Aluminum Alkyls T h e r e a r e n u m e r o u s u n c l a s s i f i e d l i t e r a t u r e references t o r e a c t i o n s y s t e m s c o n t a i n i n g o x y g e n a n d o r g a n o m e t a l l i c c o m p o u n d s , b u t v e r y f e w o f these d e a l d i r e c t l y w i t h i g n i t i o n . F o r e x a m p l e , B a m f o r d a n d N e w e t t (3) h a v e i n v e s t i g a t e d t h e k i n e t i c s a n d m e c h a n i s m of o x i d a t i o n o f d i m e t h y l z i n c a n d d i e t h y l z i n c , t r i m e t h y l a n t i m o n y a n d t r i e t h y l a n t i m o n y , t r i m e t h y l b o r o n a n d t r i p r o p y l b o r o n , a n d o t h e r s . T h e r e a r e also m a n y i n v e s t i g a t i o n s o f t h e effect o f these c o m p o u n d s o n t h e i g n i t i o n a n d c o m b u s t i o n c h a r a c t e r i s t i c s of h y d r o c a r b o n fuels. T h e g r e a t b u l k o f these d e a l w i t h l e a d a l k y l s ; h o w e v e r , reference t o o t h e r a l k y l s a n d h y d r i d e s o c c a s i o n a l l y a p p e a r s . F o r e x a m p l e , K u r z h a s r e c e n t l y p u b l i s h e d a p a p e r o n t h e influence o f d i b o r a n e o n flame speeds o f p r o p a n e - a i r m i x t u r e s (6).


179


I g n i t i o n l i m i t s f o r d i b o r a n e - o x y g e n {9) a n d e x p l o s i o n l i m i t s f o r d i m e t h y l z i n c (1) a n d t r i e t h y l b o r a n e (4) h a v e also a p p e a r e d , b u t these p a p e r s a r e m o s t l y c o n c e r n e d w i t h k i n e t i c s a n d l a c k d a t a s u c h as i g n i t i o n d e l a y v a l u e s a t v a r y i n g c o n d i t i o n s o f t e m p e r a ture a n d pressure. I n conjunction w i t h t h e synthesis p r o g r a m , previously described, t h e ignition p r o p e r t i e s o f some o r g a n o m e t a l l i c c o m p o u n d s h a v e b e e n i n v e s t i g a t e d , a n d a l i m i t e d a m o u n t o f d a t a i s a v a i l a b l e c o n c e r n i n g t h e s p o n t a n e o u s i g n i t i o n i n a i r o f a series o f organoaluminum compounds. Spontaneous ignition temperatures a n d i g n i t i o n delays are n o t absolute properties, but are strongly dependent u p o n the system i n w h i c h they are obtained. M u l l i n ( 7 ) has listed several methods i n considerable d e t a i l ; a s u m m a r y of some of the p r i n c i p a l methods is g i v e n below. Drop Methods. I g n i t i o n t e m p e r a t u r e i s t a k e n a s t h e l o w e s t t e m p e r a t u r e o f a n air-filled c a v i t y w h i c h yields i g n i t i o n w h e n drops of l i q u i d fuel are i n t r o d u c e d into i t ; t i m e i n t e r v a l s a r e m e a s u r e d , w h e n possible. T h e f o l l o w i n g t y p e s o f a p p a r a t u s h a v e been u s e d t o f o r m t h e c a v i t y : 1. A c o v e r e d c r u c i b l e i n a h e a t e d m e t a l b l o c k , i n t o w h i c h a i r i s c o n t i n u o u s l y streamed a t the block temperature ( M o o r e ) . 2. A c o n i c a l c a v i t y i s c u t d i r e c t l y i n t o a b l o c k r e p l a c i n g t h e c r u c i b l e i n N o . 1 ; t h e test i s o t h e r w i s e s i m i l a r t o M o o r e ( K r u p p ) . 3. A S T M m e t h o d D 2 8 6 - 3 0 uses a b o r o s i l i c a t e glass, c o n i c a l flask i n a g a s - h e a t e d solder b a t h ; o t h e r w i s e , i t i s s i m i l a r t o M o o r e . 4. A f o u r - c o m p a r t m e n t test s e c t i o n m e t h o d i n e a c h o f w h i c h tests a r e c o n d u c t e d a t v a r i o u s o x y g e n rates, t o d e t e r m i n e t h e effect o f v a r y i n g flow rates o f gas o n i g n i t i o n t e m p e r a t u r e . T h i s test defines a n i g n i t i o n v a l u e :

where Τ — i g n i t i o n temperature b — a f u n c t i o n of flow rate, bubbles per minute Ζ i s r e l a t i v e l y c o n s t a n t o v e r a w i d e range o f v a l u e s f o r b ( J e n z s c h ) . 5. A h e a t e d enclosure, g a s - t i g h t , i n w h i c h t h e effect o f p r e s s u r e m a y b e d e t e r m i n e d . D e s p i t e m u c h c o n t r o v e r s y r e g a r d i n g t h e exact m e a n i n g a n d usefulness o f these tests, t h e y a r e s t i l l w i d e l y u s e d . T h e p r i n c i p a l o b j e c t i o n s r a i s e d c o n c e r n t h e l a c k o f c o n t r o l o f o r d i f f i c u l t y i n q u a n t i t a t i v e l y d e t e r m i n i n g t h e v a r i a b l e s i n v o l v e d ( s u c h as fuel temperature, fuel t o a i r ratio, ignition delay, etc.). Flow Methods. T h e s e m e t h o d s g e n e r a l l y e m p l o y a h e a t e d t u b e t h r o u g h w h i c h t h e c o m b u s t i b l e m i x t u r e passes. B e c a u s e b e t t e r m i x i n g o f f u e l a n d a i r i s o b t a i n e d t h a n w i t h t h e s t a t i c m e t h o d , t h i s test o f t e n gives r e s u l t s w h i c h b e t t e r a p p r o x i m a t e those p r e v a i l i n g i n t h e a c t u a l use o f t h e f u e l . Adiabatic Compression. T h i s m e t h o d e m p l o y s r a p i d c o m p r e s s i o n o f t h e gas t o give a D i e s e l t y p e of ignition. C o m p r e s s i o n m a y be obtained b y piston compression, s h o c k t u b e s , or b y h a v i n g a i r w h i c h i s s t o r e d a t a s u f f i c i e n t l y h i g h p r e s s u r e r u s h i n t o a t u b e o f f u e l at low pressure. T h e p r i n c i p a l o b j e c t i o n s t o this m e t h o d are that the t e m p e r a t u r e a n d p r e s s u r e change c o n t i n u o u s l y and d r a s t i c a l l y d u r i n g the course of i g n i t i o n , so t h a t t h e m e a s u r e m e n t o f these v a r i a b l e s is very d i f f i c u l t . Heated Surface Method. Heated surfaces of solid o b j e c t s act as i g n i t e r s f o r c o m b u s t i b l e m i x t u r e s . These objects may be wires, rods, p a r t i c l e s , spheres, or p l a n e s . This m e t h o d not only i n t r o d u c e s a surface variable, but also leaves the temperature of the m i x t u r e n e c e s s a r y for i g n i t i o n , unknown. The v a l u e s o b t a i n e d g e n e r a l l y are h i g h e r t h a n those o b t a i n e d by t h e o t h e r m e t h o d s . 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 , the i g n i t i o n d e l a y s are so short that s p e c i a l m e t h o d s must be e m p l o y e d for their d e t e r m i n a t i o n . Such a method has been de v e l o p e d at New York University.

180



Ignition under " S t a t i c " Conditions. T h e s t a t i c i g n i t i o n tester ( F i g u r e 3 ) c o n sists o f a v e r t i c a l l e n g t h of 1 0 - i n c h I . P . S . p i p e , w h i c h h a s a ^ - i n c h steel c o v e r p l a t e

w e l d e d t o t h e t o p . A flanged c o v e r p l a t e , p o l i s h e d o n b o t h sides, seals t h e b o t t o m . T w o 2 X 10 i n c h V y c o r w i n d o w s a r e m o u n t e d v e r t i c a l l y a t t h e f r o n t a n d b a c k of t h e p i p e f o r o b s e r v a t i o n of t h e i n t e r i o r d u r i n g t e s t i n g . T h e r m o w e l l s , a i r i n l e t a n d o u t let, a n d pressure taps enter t h r o u g h the pipe w a l l . F u e l connections are i n the t o p p l a t e . T h e e n t i r e s y s t e m w h e n a s s e m b l e d is v a c u u m - t i g h t . W h e n t h e v a c u u m is b r o k e n , t h e b o t t o m c o v e r p l a t e c a n be d r o p p e d o f f ; t h i s m a k e s c l e a n i n g t h e s y s t e m r e l a t i v e l y easy.

Figure 4 . Photograph of static ignition test setup showing test chamber and window Strobolume and strip camera mounted about 3 feet in front of window T h e s y s t e m is h e a t e d a t t h e b o t t o m b y a t h e r m o s t a t i c a l l y c o n t r o l l e d h o t p l a t e a n d f o u r s t r i p h e a t e r s m o u n t e d o n t h e p i p e w a l l . T h e e n t i r e vessel i s i n s u l a t e d e x c e p t at the bottom. Temperatures are taken i n the bottom plate a n d i n the bomb interior a t t h r e e different h e i g h t s . W h e n w o r k i n g a t r e d u c e d pressures, v a c u u m i s m a i n t a i n e d b y p u m p i n g a g a i n s t a n a d j u s t a b l e l e a k r a t e of d r y a i r i n t o t h e c h a m b e r . I n t h e original system, fuel was introduced f r o m a h y p o d e r m i c syringe w h i c h was closed a t t h e b o t t o m w i t h a s y r i n g e s t o p c o c k . T h e h y p o d e r m i c needle w a s w a t e r c o o l e d a n d e x t e n d e d i n t o t h e test c h a m b e r t h r o u g h t h e t o p . A S t r o b o l u m e l i g h t source m o u n t e d i n t h e r e a r p r o v i d e d i n t e n s e l i g h t i n g a t 1 / 4 8 -



181

second i n t e r v a l s . I g n i t i o n d a t a were o b t a i n e d p h o t o g r a p h i c a l l y . O n e o f t w o t y p e s o f c a m e r a s was u s e d : 1. A s t r i p c a m e r a ( G e n e r a l R a d i o C o r p . ) i n w h i c h t h e r e i s n o f r a m e m a k e r . T h e film s t r i p moves continuously past a n image of the windows. A point of light i n t h e i m a g e a p p e a r s as a h o r i z o n t a l l i n e o n t h e f i l m . A p o i n t m o v i n g v e r t i c a l l y a p p e a r s as a n i n c l i n e d l i n e a n d a l i n e o r p l a n e o f l i g h t i n t h e w i n d o w a p p e a r s as a b a n d o n t h e f i l m . I n a d d i t i o n , e v e r y 1/48 second t h e S t r o b o l u m e l i g h t s t h e b a c k w i n d o w . I n t h i s w a y , t h e first m o m e n t o f f u e l i n j e c t i o n i s k n o w n t o 1/48 second. Ignition and propa g a t i o n of t h e flame s h o w u p as b r o a d b a n d s of l i g h t . 2. A F a s t a x , f r a m e m a k i n g , h i g h speed m o t i o n p i c t u r e c a m e r a . T h e S t r o b o l u m e is used here as a t i m i n g l i g h t o n l y . B a c k l i g h t i n g i s c o n t i n u o u s . T h e i g n i t i o n d e l a y i s calculated b y c o u n t i n g the frames f r o m i n i t i a l fuel injection t o ignition. F i g u r e 5 shows t w o s t r i p s o f a F a s t a x f i l m r e c o r d o f t h e i g n i t i o n o f t r i m e t h y l -

Figure 5. Fastax record of ignition of trimethylaluminum Conditions. 5 inches of mercury absolute air pressure and 450° F. Ignition shows in left strip, fourth frame down, 26 frames (0.013 second) after start of fuel injection. Second strip shows bomb 0.015 second after ignition a l u m i n u m a t r o o m t e m p e r a t u r e s p r a y e d i n t o a i r a t 450° F . a n d 5 inches of m e r c u r y a b s o l u t e . T h e film speed here is a b o u t 2000 f r a m e s p e r second. I g n i t i o n starts i n the f o u r t h frame d o w n , w h i c h is 26 frames after the start of injection. T h i s corresponds


182

t o a n i g n i t i o n d e l a y o f 13 m i l l i s e c o n d s (0.013 s e c o n d ) . T h e right-hand film s t r i p shows t h e b o m b w i n d o w 15 m i l l i s e c o n d s a f t e r i g n i t i o n s t a r t s ; i t c a n b e seen t h a t t h e flame fills t h e e n t i r e test c h a m b e r . F i g u r e 6 shows film r e c o r d s t a k e n w i t h t h e s t r i p c a m e r a . I n a l l p h o t o g r a p h s , t h e


A

Β

C

D Figure 6. Strip camera records of ignition of various organo metallic compounds A. B. C. D.

Tripropylboron Triethylboron without water-cooled needle Triethylboron with water-cooled needle Trimethylaluminum

i g n i t i o n shows a s w h i t e s t r e a k s . I m a g e s o f t h e w i n d o w a p p e a r e v e r y 1 / 4 8 second as w h i t e r e c t a n g l e s ; s p a c i n g differences a r e d u e t o different film speeds. F i g u r e 6, A, shows t h e i g n i t i o n o f t r i p r o p y l b o r o n ; B, t r i e t h y l b o r o n ; C, t r i e t h y l b o r o n f r o m a w a t e r c o o l e d n e e d l e ; D, t r i m e t h y l a l u m i n u m . I g n i t i o n i n F i g u r e 6, A, shows b o t t o m firing a n d m o v e m e n t o f t h e flame u p t o w a r d s t h e i n j e c t o r needle. D r o p l e t s o f f u e l c a n b e seen e n t e r i n g t h e c h a m b e r f r o m t h e t o p . Β shows n o d r o p l e t s , because t h e t r i e t h y l b o r o n flashes off as i t e n t e r s . C w i t h a w a t e r - c o o l e d needle shows t h e d r o p l e t s . D shows i g n i t i o n s t a r t i n g a t t h e t o p a l m o s t i m m e d i a t e l y (less t h a n 1 / 4 8 second) a f t e r f u e l i n j e c t i o n . B y u s i n g these test m e t h o d s , t h e i g n i t i o n d e l a y s f o r s e v e r a l o r g a n o m e t a l l i c c o m pounds have been determined ( T a b l e V ) . Table V .

Ignition Delay Values of Selected Compounds at 4 5 0 ° F. and 5 Inches of Mercury Absolute A i r Pressure Compound Dimethylaluminum chloride Trimethylaluminum Triethylaluminum Diethylaluminum bromide Diethylzinc Triethylborane Triisobutylaluminum

A series temperature experiments differential.

Ignition Delay, Second 0.020 0.013 0.040 0.150 Smoke after 0.040 0.020 Smoking only

o f s t a t i c i g n i t i o n tests w a s r u n t o d e t e r m i n e t h e effect o f p r e s s u r e a n d o n t h e i g n i t i o n c h a r a c t e r i s t i c s o f t r i m e t h y l a l u m i n u m . I n t h i s series o f i t was desirable t o have t h e fuel injected under a constant pressure T h i s was accomplished b y replacing the syringe injection system w i t h a

183


p r e s s u r i z e d feed c h a m b e r ; t h e p r e s s u r e difference across a 1 / 1 6 - i n c h c a p i l l a r y t u b e w a s k e p t a t 3 0 inches o f m e r c u r y t h r o u g h o u t t h e series o f e x p e r i m e n t s . T h e r e s u l t s o f t h i s series o f r u n s a r e s u m m a r i z e d i n T a b l e V I .


Table VI.

Effects of Temperature a n d Pressure on Ignition of Trimethylaluminum

Chamber Temp. Range, °F. 455-60 450-60 445-60 350-65

Absolute Pressure, Inches H g 2 5 30 5

Ignition Delay, Msec. 21 13 3 15

A 100° change i n a i r t e m p e r a t u r e does n o t a p p r e c i a b l y change t h e i g n i t i o n d e l a y v a l u e . H o w e v e r , t h e i g n i t i o n d e l a y decreases c o n s i d e r a b l y as t h e p r e s s u r e i s i n c r e a s e d , a n d t h i s i s t o b e e x p e c t e d , because t h e c o n c e n t r a t i o n o f o x y g e n a n d t h e h e a t i n g c a p a c i t y of t h e a i r t h r o u g h w h i c h the s p r a y travels are increased.

Acknowledgment M u c h of the work o n compatibility w i t h materials of construction was performed for M a n n i n g , M a x w e l l a n d M o o r e , I n c . , D a n b u r y , C o n n . , a n d t h e a u t h o r s w i s h t o express t h e i r a p p r e c i a t i o n f o r p u b l i c a t i o n p e r m i s s i o n .

Literature Cited (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)

Badin, Ε., Walters, Ο., Pease, R., J. Am. Chem. Soc. 69, 2586 (1947). Bamford, C. H., Levi, D. L., Newett, D. M., J. Chem. Soc. 1946, 468. Bamford, C. H., Newett, D. M . , Ibid., 1946, 688, 695. Brokaw, R., Badin, Ε., Pease, R., J. Am. Chem. Soc. 70, 1921 (1948). Grosse, Α. V., Mavity, J. M . , J. Org. Chem. 5, 106 (1940). Kurz, P. F., Ind. Eng. Chem. 48, 1863 (1956). Mullin, B. P., "Spontaneous Ignition of Liquid Fuels," Agardograph No. 4, Butterworth's Scientific Publications, London, 1955. Pitzer, K . S., Gutowski, H . S., J. Am. Chem. Soc. 68, 2204 (1946). Roth, W., Bauer, W. H., "Combustion of Diborane-Oxygen Mixtures at the Second Explosion Limit," Fifth Symposium on Combustion, p. 710, Reinhold, New York, 1955. Ziegler, K., Angew. Chem. 64, 323, 330 (1952). Ziegler, K., Gellert, H . G., Martin, H., Nagel, K., Schneider, J., Ann. Chem. 589, 91 (1954).

(12) Ziegler, K., Gellert, H . G., Zosel, K., Lehmkuhl, W., Angew. Chem. 67, 424 (1955). RECEIVED for review May 10, 1957. Accepted July 1, 1957.

Preparation and Ignition Properties of Aluminum Alkyls - Advances in

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