Subject: CHEM GUY's notes on birch like reductions and related whatnot,...

My notes on Birch-like reductions
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Aurther Birch wrote about the reduction of benzyl alcohols in "The Journal
of the Chemical Soceity" (1945 page 809) . His procedure was to have the
benzyl alcohol dissolved in an amine-alcohol solution and then add the
alkali metal. The molar product yeild was about 75% for carbinol
Note: The ammonia was "about 30 times the volume of alcohol".

The Journal Of Organic Chemistry, Vol 40, 1975, page 3152 describes the
birch method of benzyl alcohol reduction as so:

"SODIUM-AMMONIA-ETHANOL. To a stirred mixture of 771 mg (4.99 mmol) of
tetralol and 500 mg (10.96 mmol) of EtOH in 20 mL of NH3 was added six
peices of Na (253 mg, 11 mg-atoms) over a 14 minute period to maintain a
dark blue solution. Approximately 12 minutes later the mixture turned white
and then the NH3 was allowed to evaporate. Work up as described above
yeilded a mixture of tetralin (75%) and 5,8-dihydrotetralin (25%)."

Now the same article in JOC lists a table of several benzyl alcohols and
their product yeilds. All the fused cyclic alcohols and ring substitued
benzyl alcohols have a low yeild with the Na-EtOH-NH3 method but the other
single phenyl alcohols have a yeild around 100%. Never does the article
refer to ephedrine but through analogy you can see that the Na-EtOH-NH3
method has its merits.

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This is from "The Journal Of Organic Chemistry", Vol. 28, page 1094
The authors are: Robert A. Bensker, Merwyn L. Burrous,
James J. Hazdra, and Edwin M. Kaiser

"... In the course of this paper we are reporting the effects of water and
 alcohols on the course of the [Li-amine] reduction."
"We found that, in the presense of alcohol, the Li-amine combonation
can be used quite sucessfully to form dihydro aromatics."
"The soduim-ammonia-alcohol system is not capable of reducing an
unconjugated double bond except in certain isolated systems.  The
same is not true of the Li-amine system, which is capable of 1, 2
reductions of olfeins.  Hence, with excess metal, the 2, 5 dihydro
products can suffer a slow reduction of one double bond in the
Li-amine system, thereby forminga 1-substituted olefin. In the Birch
method excess metal (e.i., more than 2 equivalents based on the
aromatic) can be used without fear of further reduction..."
"Interestingly enough, the presense of 3 equivalents of ethanol
was not capable of stopping the Li-amine reduction at the dihydro
stage in the presence of 6 equivalents of metal."
"Even 6 equivalents of ethanol did not prevent this isomersation
 entirly in the presence of 6 equivalents of Li, since 26% of the
product in this case was 1-isopropylcyclohexene.  Albeit, the major
product was 2,5-dihydrocumene."[ 64% ]
"The reaction in this case was quite exothermic and the metal was used
 up entirely in about 4 hours.  Obviously much of the metal consumed
was by direct reaction with the alcohol to form hydrogen.  The results
clearly indicate the necessity of controlling the quanity of Li used
if one desires to prepare the unconjugated diene to the virtual
exclusion of 1-substitued olefin by the Li-amine system."
"A similar observation was noted when an attempt was made to reduce
cumene in methylamine was water as the protn donator rather than an
alcohol.  In this case only 4 equivalents of metal were used, but
still monoolefins were produced..."
"One must conclude that the water was not able to prevent diene
conjugation, ..."
"It is at first sight startling that Li-amine reductions can be carried
out successfully in the presence of water.  This clearly indicates the
extreme ease and rapidity with which electron transfer from the Li to
the aromatic and its diene intermidiates occurs in this system.
 Obviously these organic species are competeing successfully for
electrons with the hydrogen of the water molecules."

The reduction of isopropylbenzene. The birch reduction with sodium gets 92%
2,5 dihydroisopropylbenzene. The Li-amine gets 88% 2,5
dihydroisoproplylbenzene.

NOTE:This method (Li-amine) still can over reduce as show by this example,
but it illustrates how sucessfully the aromatic competes for the electron
with the water.

When the reduction of isopropylbenzene takes place with out water, with a
trace of water, and with 2 eqivalents of water in MeNH2 and with 4
equivalents of Li.

W/O H2O-100% isopropylhexene

with a trace of H2O- 100% "

With 2 equivalents H2O- 93% "

Also this the results from using 6 equivalents of Li in the presence and
absence of ethanol in EtNH2

Pure EtNH2- 71% isopropylhexene and 29% isopropylhexane

3 equivalents EtOH- 77% isopropylhexene and 23 isopropylhexane

6 equivalents of EtOH- 30% isopropylhexene, 2% isopropylhexane and 64%
dihydro-isopropylbenzene.

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>From "Electrons in Liquid Ammonia" by J.C. Thompson, 1976

"The fact that dilute solutions containing equivalents amounts of
alkali and alkaline metals give virtually the same near-infrared
absorption spectra indictaes the presence of a common absorbing species
which must be described without reference to the cation.  Indeed,
dilute solutions of solvated electrons electrochemically generated
in the presence of tetraalkylammonium ions with widely-varying
structural parameters are also optically indistinguishable from
those formed by the dissolution of metal atoms."

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>From "The Journal of Chemical Physics", Vol 44, number 6,
page 2297, 15 march 1966.

"...The approximate times necessary at -78C for the optical density
due to the solvated electron to decay to one half its initial value
were 8, 20, 8, and 25 mirco-sec for methanol, ethanol, isopropanol,
and n-butanol, respectively.  These half-times are 10 to 20 times
 longer than the corresponding values at room tempature."
"... at -78C, absorptions due to the solvated electron were obtained
for monomethylamine (T[.5]= 3 mirco-sec) and monoethylamine
(T[.5]= 3.5 mirco-sec).  At -110C the absorption of the solvated
electron in diethylether was obtained (T[.5]= 2 mirco-sec)."

Here is a condensed table of the half-life of the solvated electron,
(T[.5]), in various solvents: (From the same work as above)

SUBATANCE/HALF-LIFE IN MIRCO-SECONDS
[all measuements at 25C unless otherwise stated]
100% glycerol / .44 micro-sec
63% glycerol- 37% water / .75
47% " - 53% " / .9
32% " - 68% " / 1.6
19% " - 1% " / 1.5
8.3% " - 92% " / 1.3
53% water - 47% ethanol / 3.4
36% " - 64% " / 2.2
20% " - 80% " /  2.5
10% " - 90% " / .40
50% ethylene glycol - 50% water / .85 @ 20C
10% " - 90% " / .6 @ 20C
70% methanol - 30% water / 2.7
79% isopropanol - 21% water / .7 @ 20C
70% " - 30% " / .65 @ 20C
31% glycerol - 69% ethanol / .5
12% " - 88% " / .75
50% methanol - 50% isopropanol / 10 @ -78C

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>From "Ionizing Solvents" by I. Junder 1970
from a table and its amendments concerning the solublities
of compounds in liquid ammonia.

"NaOH....i[meaning insoluble in liquid ammonia]
Na2SO4...i
(NH4)2SO4...i"
"Alcohols: Simple and polyfunctional alcohols are miscible with liquid
ammoina.  Phenols are also soluble.

Ethers: Diethylether is moderately soluble [in liquid ammonia].
Ethers having higher molecular weights are not very soluble.

Hydrocarbons: Alkanes are insoluble, while alkenes and alkynes
 are slightly soluble.  Benzene dissolves readily."

"All solutions of metals in liquid ammonia are metastable, though they
can be stored for long periods in the absence of catalysts
(impurities).  Catalysts and in paticular finely divided metals
(platium asbestos, platium sponge, and raney nickel), favour
decompostion in accordence with: [where x is a number]
M + x NH3 --> M(NH2)x + (x/2)H2
This decompostion is used for the preparation of alkali and alkaline
earth metal amides (amide reaction).  It corresponds to the reaction
of alkali metals with water.  The catalytic activity of many metal
salts (particularly iron salts) is due to the fact that the salt is
 first reduced and the resulting finely divided metal catalyses the
amide formation."

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Solublities of group 1 and 2 metals in solvents
*****************************************************************

This is (between the __ lines) generated from an article called "The
Solublity of Alkali Metals in Ethers" in the Journal of the Chemical
Soceity, April 1959, page 3767.
________________________________________________________________

 As the solutions were unstable to air they were handled in vacuo
or in oxygen free nitrogen methods.

Dimethyl Ethylene gycol ether.
Na/K - very soluble
K - moderate
Na, Li, Ca - None

Ethyl Methyl Ethylene Glycol ether
Na/K - slight

Dimethyl Diethylene glycol ether
Na/K - very soluble

Diethyl Diethylene Glycol ether
Na/K - slightly

Ethyl Methyl Diethylene Glycol ether
Na/K - Moderate

Methyl n-propyl Diethylene Glycol ether
Na/K - slightly (a)

n-Butyl Methyl Diethylene Gycol ether
Na/K - very slightly (a)

TetraHydroFuran
Na/K - slightly

1-Methoxymethyltetrahydrofuran
Na/K - Very soluble

1-ethoxymethyltetrahydrofuran
Na/K - moderate (b)

2-Methyltetrahydrofuran
Na/K - very slightly (a)

Dioxan
Na/K - None

Cyclic tetramer of propylene oxide
Na/K - Very soluble

1: 2-Dimethoxypropane
Na/K - very slightly (a)

Triethylene glycol dimethyl ether
Na/K - very soluble

Tetraethylene glycol dimethyl ether
Na/K - very soluble

Ethylenediamine
Na/K - very soluble

Methoxyethylamine
Na/K - very soluble

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a = (only on proplonged cooling to 193 K)
b = ( slightly at room temp; moderate on cooling to 193 K)
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This article goes on to state:

Lithium- doesn't dissolve in dimethylamine but is
quite soluble in ethylamine

"(d) CH3-(OCH2CH2)n-OCH3  As n increases from 1 to 4 there is a very marked
increase in solublity owing to an increase in the number of donor atoms
per ether molecule.  Entropy effects of chelation will evidently become
more pronounced as n increases."
________________________________________________________________________

>From "Ionizing Solvents", by I. Junder, yr 1970, page 39

Lithum dissloves 10.9 gr in 100 gr of NH3 at -33 C
Sodium dissolves 24.8 gr in 100 gr of NH3 "
Potassium dissolves 46.4 gr in 100 gr of NH3 "

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U.S. Patent # 5675038 states:
Alkali metals dissolve in polyamines.
 For example: EDA, ethylenediamine, H2N-CH2CH2-NH2.

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>From "Non-aqeous Solvents", by John R. Chipperfield, copyright
 1999, page 60,

"HMPA (hexamethylphosphoramide) dissolves group 1 metals in a similiar
 way to liquid ammonia, amines and ethers, forming deep blue solutions,
 but only low concentrations of solvated electrons can be prepared.
..."

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