Melgar
Anti-Spam Agent
Posts: 2004
Registered: 23-2-2010
Location: Connecticut
Member Is Offline
Mood: Estrified
|
|
Reduction with alkali metal and alcohol
The attached document indicates that sodium metal and ethanol (as well as other alcohols) can perform quite a range of interesting reductions, such as
nitriles and oximes to amines, ketones to alcohols, certain alkenes to alkanes, esters to alcohols, and even some aromatic rings.
It doesn't reduce nitro groups since it just forms the sodium salt and hydrogen when reacted with nitroalkanes, and it forms an opaque reddish-brown
substance when reacted with nitroalkenes.
It does seem like a very useful type of reduction especially for anyone that doesn't have access to sodium borohydride, and the description says that
this combination is often used industrially instead of lithium aluminum hydride for certain things. It's not very dangerous either, if you do it in a
flask with some sort of cap or lid that you can put on loosely so that the evolving hydrogen can escape without letting in oxygen.
Now, I guess a follow-up question would be, how would lithium react differently? It doesn't seem to react as vigorously, but I've heard it's a better
reducing agent in some reactions, though I'm having a hard time finding out which ones. I guess, what would be the determining factor?
Also, what can sodium amalgam do that sodium in alcohol can't?
Attachment: sodium-metal-reduction.pdf (62kB)
This file has been downloaded 632 times
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
|
|
|
Loptr
International Hazard
Posts: 1347
Registered: 20-5-2014
Location: USA
Member Is Offline
Mood: Grateful
|
|
Another interesting reagent is magnesium and methanol.
http://www.sciencemadness.org/talk/files.php?pid=451913&...
I have seen references to it being used to reduce cinnamic acid to hydrocinnamic acid, which is beyond the abilities of NaBH4, too.
"Question everything generally thought to be obvious." - Dieter Rams
|
|
|
Corrosive Joeseph
National Hazard
Posts: 915
Registered: 17-5-2015
Location: The Other Place
Member Is Offline
Mood: Cyclic
|
|
Sodium from Mg, NaOH, H2SO4 and Antifreeze for anyone who has missed these recent happenings...........
Nurdrage - "Make Sodium Magnesium Oxide Aggregate - A Substitute for Sodium Metal"
https://www.youtube.com/watch?v=ZXCSL0r4aqg&app=desktop
followed by more Nurdrage - "Make Sodium Metal Without Electrolysis Using Domestic Chemicals"
https://www.youtube.com/watch?v=jCrFFVVcPUI
I looked into this lately and many patterns and similarities were noted.
It seems dryness and purity of the alcohol coupled with a rapid vigorous reaction is key for good yields.........
[EDIT] - Found some notes
Usual ratios per 1 mole of substrate are about 7 to 11 moles of sodium, 10 seems to be common practice, and it is recommended to experiment by
increasing sodium until yields level off.
3 to 4 moles of alcohol is used per mole of substrate........
"Ethanol is usually used, although higher alcohols are preferable because of their higher boiling points"
From - "Preparative Organic Chemistry" by Weygand and Hilgetag"
"The use of higher molecular weight alcohols has been reported to afford better yields of products."
From - "Sugden, J. K.; Patel, J. J. B., Chem. Ind. (London) 1972, 683"
"Many reductions with sodium are carried out in boiling alcohols: in methanol, ethanol, 1-butanol, and isoamyl alcohol. More intensive reductions are
achieved at higher temperatures. For example, reduction of naphthalene with sodium in ethanol gives 1,4-dihydronaphthalene, whereas in boiling
isoamyl alcohol tetralin is formed. You need a large excess of sodium for reductions in boiling alcohols. A better procedure is to carry out such
reductions by adding a stoichiometric quantity of an alcohol and the compound to bee reduced in toluene or xylene to a mixture of toluene or xylene
and a calculated amount of a dispersion of molten sodium."
From - "Reductions in Organic Chemistry" by Milos Hudlicky
"Therefore, all further experiments were carried out above 100 °C (sodium mp 98 °C) and at approximately 250?500 rpm, avoiding such problems by
handling only liquid sodium. No stirring was applied during the melting of sodium. A related behavior was reported for sodium in n-butanol: at
temperatures below 100 °C, sodium butoxide formation outweighed the desired reduction."
From - "Scale-up of an Oxime Reduction with Melted Sodium in Standard Pilot-Plant Equipment"
(Ref available on request)
"The Bouveault-Blanc reduction (1) is the oldest reduction of esters to alcohols, it is carried out by adding sodium into a solution of an ester in
ethanol, the yeilds were low, possibly due to side reactions such as claisen condensation. With some modifications, good yeilds (65-75%) were
obtained with esters of mono-carboxylic acids (2), dicarboxylic acids (73-75%) (3), and even unsaturated acids containing nonconjugated double bonds
(49-51%) (4). The main improvement was use of an inert solvent such as toluene or xylene and a secondary alcohol that is acidic enough to decompose
sodium containing intermediates but does not react to rapidly with sodium: the best of all is methylisobutylcarbinol (4-methyl-2-pentanol). Under
these conditions the precise theoretical amounts of sodium and the alcohol may bee used, and this precision prevents side reactions such as acyloin
and Claisen condensations. The reaction is best carried out by adding a mixture of sodium and xylene at a rate sufficient to maintain reflux. Yeilds
with this modification are close to theoretical or at least 80%"
From - https://the-hive.archive.erowid.org/forum/showflat.pl?Cat=&a...
"Yields are poor if the ethanol is not completely dehydrated. A very satisfactory grade of alcohol is obtained by distilling ordinary absolute alcohol
from magnesium methoxide"
"The best yields are obtained when the reduction is carried out rapidly."
From - http://www.orgsyn.org/demo.aspx?prep=CV2P0318
"The grade of absolute alcohol used in the reduction is very important. Ethanol dried with magnesium methoxide (Org. Syn. Coll. Vol. I, 1941, 249) was
used in this preparation. Alcohol dried over lime gives very low yields."
" The best yields are obtained when the reductions are carried out rapidly. If the reaction seems to be about to get out of control, the stirrer is
stopped and the mixture is cooled with an ice pack."
"As soon as the alcohol begins to boil, the steam is shut off and the temperature is maintained by introducing strips of sodium through the top of the
condenser. The total amount of sodium added is 500 g., and it should be added as rapidly as is possible without loss of alcohol. The last 150 g. of
sodium melts in the hot mixture and may be added very rapidly without loss of alcohol or amine."
From - http://www.orgsyn.org/demo.aspx?prep=cv2p0372
"The purity of the absolute ethanol is of prime importance. Ethanol dried only by a lime process gives a low yield (20–25%). The ethanol used in
this procedure was dried over lime and then over aluminum tert-butoxide, after which it was distilled directly into the flask used for the reaction."
From - http://www.orgsyn.org/demo.aspx?prep=cv3p0671
"Commercial butyl alcohol is dried by distillation through a 1-m. column, and the portion boiling at 117.5–118.5° is used. The ordinary commercial
alcohol is usually sufficiently pure so that the bulk of the alcohol remaining in the flask after the temperature at the top of the column reaches
117° need not be distilled but may be used directly for the reduction."
"If one wishes to reduce this time, external heat may be applied until the boiling point is reached. In a run in which the butyl alcohol was heated to
boiling before the addition of the sodium, the reaction began more vigorously but the yield was practically unchanged."
"The reaction mixture should not be cooled below the boiling point of the butyl alcohol as a continuously vigorous reaction is essential for good
yields."
From - http://www.orgsyn.org/demo.aspx?prep=cv2p0468
Anothter experimental (I was only reading last night but the ref escapes me right now) recommended adding all the sodium to the boiling alcohol/oxime
solution as quickly as was possible without loss of vapour out the condenser and then to add heat as to never let the reaction slacken. It was then
refluxed for a period of time. This, they claimed, increased yields.
"1. Absolute Alcohol.—Good absolute alcohol is essential. The use of alcohol of about 98 per cent gives only about two-thirds the yields obtained
with absolute alcohol. Alcohol dried over lime usually runs about 98.5–99.5 per cent. A good method of obtaining a higher grade of absolute alcohol
is to treat this alcohol with a little sodium. When the sodium has dissolved, the alcohol is distilled from a steam bath. Under these conditions, any
trace of water that may be present on account of the equilibrium remains in the concentrated solution of sodium ethoxide and sodium hydroxide. See,
also, p. 249 and, Note 1, on p. 251."
Taken from - http://www.orgsyn.org/demo.aspx?prep=CV1P0258
Over and out..........
/CJ
[Edited on 6-8-2017 by Corrosive Joeseph]
Being well adjusted to a sick society is no measure of one's mental health
|
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
