moo
(Hive Bee)
11-01-03 01:05
No 468077
       Oxidations and brominations w/ H2O2/Br2/HBr
(Rated as: excellent) 		    

I ran into a nice article. cool
 
Too bad they didn't try to oxidise/brominate any toluenes with only electron donating substituents even though it is quite obvious that ring bromination is going to happen. Maybe this "side reaction" could be exploited to get 4-bromo-2,5-dimethoxybenzyl bromide or 4-bromo-2,5-dimethoxybenzaldehyde straight from 2,5-dimethoxytoluene.
 
Also, it's interesting that cumene yields alpha-methylstyrene and alpha-methyl-beta-bromostyrene. It might be naive to think that the latter product could be hydrolysed to 2-phenylpropanal with an alkali metal hydroxide knowing how stable aldehydes are. In that case one has to settle for only one P2P precursor (../rhodium /2-phenylpropanal.html).  Maybe the reaction could be tweaked to produce P2P and 2-phenylpropanal from cumene in one pot, who knows? In the end the yields are sure going to suck.
 

Catalytic Processes of Oxidation by Hydrogen Peroxide in the Presence of Br2 or HBr. Mechanism and Synthetic Applications
Amati, Alessandro; Dosualdo, Gabriele; Zhao, Lihua; Bravo, Anna; Fontana, Francesca; Minisci, Francesco; Bjorsvik, Hans-Rene
Organic Process Research & Development 2(4), 261-269 (1998) (../rhodium/pdf /br-cat.h2o2-oxidation.pdf)
DOI:10.1021/op980028j
 
Abstract
The mechanism and the synthetic applications for the oxidation of alcohols ethers, and aldehydes by H2O2 catalyzed by Br2 or Br- in a liquid two-phase system (aqueous and organic) are reported.  Aliphatic and benzylic primary alcohols and ethers show an opposite behavior, which has been rationalized on the ground of the different electronic configurations of the intermediate alkyl (p-type) and acyl (s-type) radicals and their influence on enthalpic and polar effects. A two-phase system is particularly useful also for an efficient benzylic bromination by Br2 or Br-; the substitution of the benzyl bromide by OH, OR, and OCOR regenerates Br-, which can be recycled. The evaluation of the relative reactivities of the involved substrates and intermediates has allowed to develop a variety of simple, facile, convenient, and selective syntheses of alcohols, aldehydes, ketones, esters, and benzyl bromides, which fulfill the conditions for practical applications.
 
 
General Oxidation Procedures.
 
Oxidation of Primary Aliphatic Alcohols to Esters. (I suppose this is procedure A)
Five millimoles of the alcohol, dissolved in 7.5 mL of CH2Cl2, was stirred for 2 h at room temperature with 3 mmol of Br2 and 7.5 mL of water; 6 mmol of H2O2 (30% aqueous solution) was added within 2 h. The organic phase was separated, washed with aqueous NaHCO3 solution, and analyzed by GC (ethyl heptanoate as internal standard). The reaction products were identified by GC-MS analysis and by comparison with authentic samples. The results are reported in Table 1. The aqueous solution, containing HBr, has been utilized for a further oxidation of 5 mmol of alcohol in 7.5 mL of CH2Cl2 by the addition of 7.5 mmol of H2O2 over 4 h: the results are quite similar.
 
Oxidation of Secondary Alcohols to Ketones
Procedure A was utilized by employing half of the oxidant. The results are reported in Table 2.
 
Oxidation of Aliphatic Aldehydes in the Presence of Alcohols
Five millimoles of the aldehyde, 15 mmol of the alcohol, and 2.5 mmol of Br2 dissolved in a mixture of 7.5 mL of CH2Cl2 and 7.5 mL of water were refluxed for 1 h; 2.5 mmol of H2O2 was added, and the mixture was refluxed for an additional hour. The organic phase was separated and analyzed by GC and GC-MS; authentic samples were utilized for the identification and analysis of the reaction products. The results are reported in Table 3.
 
Oxidation of Benzyl Alcohols to Aldehydes
Two millimoles of the alcohol, dissolved in 10 mL of ACOEt and mL of water, together with Br2 and H2O2 in the ratios reported in Table 6, was refluxed for 4 h. The organic phase was separated, washed with aqueous NaHCO3 solution, and analyzed by GC (p-chlorobenzaldehyde as internal standard; with p-chlorobenzyl alcohol, o-chlorobenzaldehyde was utilized as internal standard). The reaction products were identified by GC-MS analysis and by comparison with authentic samples. The results are reported in Table 6.
 
Oxidation of Benzyl Alcohols to Methyl Benzoate (Procedure E)
Five millimoles of benzyl alcohol, 20 mmol of CH3OH, and mmol of Br2 in 10 mL of CH2Cl2 and 10 mL of water were refluxed for 2 h; 6 mmol of H2O2 were then added under reflux over a 2 h period. The organic phase was separated and analyzed by GC (ethyl benzoate as internal standard) by using authentic samples and GC-MS analysis for the identification of the reaction products. The results are reported in Table 7.
 
Oxidation of Benzyl Alcohols to Alkyl Benzoates (Procedure F)
Procedure E has been utilized with benzyl alcohols and tertiary aliphatic alcohols. With primary aliphatic alcohols, the procedure has been modified as follows: 5 mmol of benzyl alcohol, 1 mmol of aliphatic alcohol, and 5 mmol of Br2 in 10 mL of CH2Cl2 and 10 mL of water were refluxed. Over 4 h, 6 mmol of H2O2 and 4 mmol of aliphatic alcohol were added. The organic phase was separated and analyzed by GC and GC-MS. The results are reported in Table 8.
 
Oxidation of Aromatic Aldehydes to Alkyl Benzoates
Procedures E and F were utilized by using half of the oxidant. The results are reported in Table 9.
 
 
Oxidation of Ethers
Alkylbenzyl Ethers. Two millimoles of methyl benzyl ether in 7.5 mL of CH2Cl2 were stirred for 24 h at room temperature with 0.2 mmol of Br2 and 4 mmol of H2O2 (30% aqueous solution). The mixture was analyzed during the reaction course after 0.5, 1.3, 2, 3, 5.5, and 26.5 h, and the results are reported in Table 10.
Di-n-alkyl Ethers. Two millimoles of di-n-alkyl ether, 0.2 mmol of Br2, and 4 mmol of H2O2 (30% aqueous solution) were stirred for 4 h at room temperature in 7.5 mL of CH2Cl2. The organic phase was separated and analyzed. The results are reported in Table 12.
 
Oxidation of Tetrahydrofuran (THF) to gamma-Butyrolactone
Ten millimoles of THF and 4 mmol of Br2 were refluxed for 1 h in a mixture of 5 mL of CH2Cl2 and 5 mL of water. Four millimoles of H2O2 was added, and the mixture was refluxed for 1 h; an additional 4 mmol of H2O2 was added, and the mixture was refluxed for 2 h. The mixture was analyzed after 1, 2, and 4 h, and the results are reported in Table 13.
 
The same procedure was utilized with other ethers, and the results are summarized in Table 13.
 
 
Bromination of Alkylbenzenes
Five millimoles of alkylbenzene, dissolved in 15 mL of a CH2Cl2/H2O mixture containing the other reagents in the ratios reported in Tables 14 and 15, were refluxed for 4 h. The CH2Cl2 solution was separated from the aqueous phase and directly analyzed by GC and GC-MS, by using p-chlorobenzyl bromide as internal standard (with p-chlorotoluene the internal standard was o-chlorobenzyl bromide) and authentic samples of the benzyl bromides for the characterization. With substrates deactivated by the presence of -NO2, -CN, and -COOR groups, H2O2 was slowly added to the reacting mixture. In competitive bromination of equimolar amounts of o-nitrotoluene and toluene, only the latter is substantially brominated. With cumene, only 5% of cumyl bromide was formed; the main reaction products were alpha-methylstyrene (72%) and a 1:1 mixture of cis- and trans-alpha-methyl-beta-bromostyrenes (21%). The products were characterized by comparison (GC-MS) with authentic samples.


Table 1. Oxidation of primary aliphatic alcohols to esters by H2O2, catalyzed by HBr
alcohol solvent time (h) conversion (%) yield (%)a
1-propanol CH2Cl2/H2O (1:1) 2 56 99
1-propanol CH2Cl2/H2O (1:1) 4 69 98
1-propanol CH2Cl2/H2O (1:1) 6 100 98
1-butanol CH2Cl2/H2O (1:1) 2 58 99
1-butanol CH2Cl2/H2O (1:1) 4 71 98
1-butanol CH2Cl2/H2O (1:1) 6 100 98
1-pentanol CH2Cl2/H2O (1:1) 6 100 97
1-hexanol CH2Cl2/H2O (1:1) 6 100 98
2-methyl-1-pentanol CH2Cl2/H2O (1:1) 6 100 95
1-heptanol CH2Cl2/H2O (1:1) 6 100 98
1-heptanol hexane/H2O (1:1) 6 61 97
1-heptanolb hexane/H2O (4:1) 6 58 95
1-heptanolc hexane/H2O (4:1) 24 91 91
1-heptanol AcOEt/H2O (1:1) 4 20 57
1-decanol CH2Cl2/H2O (1:1) 6 100 97
a Based on the converted alcohol. b 5% of heptanal is formed. c 9% of heptanal is formed.
 
 
Table 2. Oxidation of secondary alcohols to ketones by H2O2, catalyzed by Br2
alcohol conversion (%) yield (%)a
2-hexanol 100 96
2-heptanol 98 99
2-decanol 99 98
cyclohexanol 94 87
cyclopentanol 96 91
2-adamantanol 100 96
Ph-CHOH-CH3 100 95
Ph-CHOH-Ph 98 88
a Based on the converted alcohol.


Table 3. Oxidation of aliphatic aldehydes to esters in the presence of primary and tertiary alcohols
aldehyde alcohol conversion (%)a yield (%)b
1-heptanal n-BuOH 96 92
1-heptanal 1-AdOH 89 87
1-heptanal t-BuOH 92 84
1-pentanal n-PrOH 87 91
1-pentanal n-BuOH 91 89
1-pentanal t-BuOH 83 87
a Converted aldehyde. b Based on the converted aldehyde.

 
Table 6. Synthesis of aldehydes X-C6H4-CHO from X-C6H4-CH2OH by bromine-catalyzed H2O2 oxidation
X ratio (alcohol:Br2:H2O2) conversion (%)a yields (%)b
H 1:0.05:2 92 98
H 1:0.15:1.5 100 93
o-Me 1:0.15:2 97 91
m-Me 1:0.15:2 94 96
p-Me 1:0.15:2 98 90
o-Cl 1:0.15:2 98 93
p-Cl 1:0.05:2 99 97
p-Cl 1:0.15:1 94 93
p-Br 1:0.05:2 98 98
p-COOEt 1:0.15:2 93 94
p-CN 1:0.2:2 94 92
o-NO2 1:0.2:2 94 96
p-NO2 1:0.15:2 81 95
p-Ph 1:0.15:2 98 94
a Conversion of the benzyl alcohol. b Yields based on the converted alcohol.


Table 7. Oxidation of benzyl alcohols X-C6H4-CH2OH to the corresponding methyl benzoates
X conversion (%) yields (%)a
H 100 87
o-Me 100 83
p-Me 100 88
o-Cl 93 83
p-Cl 92 86
a Based on the converted benzyl alcohol.


Table 8. Oxidation of benzyl alcohols X-C6H4-CH2OH to alkyl benzoates X-C6H4-COOR
X R-OH conversion (%)a yields (%)b
H EtOH 93 84
H n-BuOH 86 82
H t-BuOH 91 93
o-Cl n-BuOH 97 83
p-Cl n-BuOH 92 88
o-Me n-BuOH 98 81
o-Me t-BuOH 78 94
p-Me t-BuOH 81 96

a Conversion of benzyl alcohol. b Yields based on the converted benzyl alcohol.
fear fear hate hate 		 
 
 
 
    moo
(Hive Bee)
11-01-03 01:13
No 468078
       Oxidations and brominations w/ H2O2/Br2/HBr
(Rated as: good read) 		    

Table 9. Oxidation of aromatic aldehydes, X-C6H4-CHO, to alkyl benzoates X-C6H4-COOR
X R-OH conversion (%)a yields (%)b
H MeOH 92 96
H EtOH 94 84
H n-BuOH 87 83
H t-BuOH 72 94
o-Cl MeOH 93 9
p-Cl MeOH 91 89
o-Me MeOH 92 87
p-Me MeOH 89 91
p-Me n-BuOH 91 78
p-Me t-BuOH 81 96
a Conversion of aldehyde. b Yields based on the converted aldehyde.
 
 
Table 10. Oxidation of benzyl methyl ether to benzaldehyde (I), methyl benzoate (II), and mixed anhydride between benzoic and formic acids (III)
T (°C) reaction time (h) conversiona (%) I (%)b II (%)b III (%)b
18 0.5 18 87 0 0
18 1.3 32 91 2.1 0
18 2 48 89 5.3 0
18 3 70 87 9.1 0
18 5.5 99.5 81 18.3 0
18 26.5 100 20 60 0
42 2 100 33 40 25
42 4 100 0 61 32
a Conversion of benzyl ether. b Yields based on the converted benzyl ether.
 
 
Table 11. Oxidation of secondary benzyl ethers, X-C6H4-CH(R)-OMe, to the corresponding ketones, X-C6H4-CO-R
X R conversiona (%) yieldsb (%)
H Me 98 94
H Et 96 97
o-Cl Me 97 92
p-Cl Et 99 89
o-Me Me 96 91
p-Me Me 92 94
p-Me Et 96 98
a Conversion of benzyl ether. b Yields based on the converted benzyl ether.
 
 
Table 12. Oxidation of dialkyl ethers, R-CH2-O-CH2-R, to the corresponding esters, R-COOCH2R (IV)
R conversion (%) IVa (%) R-CH2OHa (%) R-COOHa (%)
n-Pr 94 65 10 8
n-Bu 92 73 7 6
n-hexyl 91 71 8 7
2-Me-pentyl 87 70 6 9
n-heptyl 89 71 9 8
a Yields based on the converted ether.
 
 
Table 13. Oxidation of THF and other ethers
ether product time (h) conversion (%)a yield (%)b
THF gamma-butyrolactone 1 34.2 98
THF gamma-butyrolactone 2 64.6 87
THF gamma-butyrolactone 4 92.4 81
methyl cyclooctyl ether cyclooctanone 4 87 92
methyl cyclooctyl etherc cyclooctanone 4 96 97
dicyclohexyl ether cyclohexanone 4 98 93
methyl cyclohexyl ether cyclohexanone 4 91 96
a Conversions based on the oxidant. b Yields based on the conversion. c The procedure is the same, with the difference that a stoichiometric amount of Br2 was used in a two-phase system in the absence of H2O2.
 
 
Table 14. Bromination of 2-nitrotoluene (Ar-CH3)
brominating agent ArCH3:Br:H2O2 solvent conversion (%) yields (%) of ArCH2Bra
Br2 1:1:0 CH2Cl2 traces traces
Br2 1:0.5:0 CH2Cl2/H2O 1:1 20 99
Br2 1:1.2:0 CH2Cl2/H2O 1:2 91 89
Br2/H2O2 b 1:0.7:0 CH2Cl2 93 94
Br2/H2O2 1:0.5:0.5 CH2Cl2/H2O 1:1 34 98
Br2/H2O2 1:0.7:10 CH2Cl2/H2O 1:1 8 100
Br2/H2O2 c 1:0.7:1 hexane/H2O 1:1 0 0
HBr/H2O2 1:2:2 CH2Cl2/H2O 1:2 87 93
a Based on the converted 2-nitrotoluene. b 36% aqueous H2O2. c 2- and 3-Bromohexanes are formed.
 
 
Table 15. Bromination of alkylbenzenes substrate
(S) brominating agent S:Br:H2O2 solvent conversion (%) yields (%)a
toluene Br2/H2O2 1:0.7:1 CH2Cl2/H2O 1:1 93 94
tolueneb Br2/H2O2 1:1:1 CH2Cl2/H2O 1:1 100 70
toluene NaBr/H2O2/H2SO4 (1) 1:2:2 CH2Cl2/H2O 1:1 96 92
ethylbenzene Br2/H2O2 1:0.7:0.5 CH2Cl2/H2O 1:1 87 92
ethylbenzene NaBr/H2O2/H2SO4 (1) 1:2:2 CH2Cl2/H2O 1:1 91 94
ethylbenzene Br2/H2O2 1:2:1.5 CH2Cl2/H2O 1:1 93 89
cumenec Br2/H2O2 1:0.7:0.5 CH2Cl2/H2O 1:1 60 5
p-CN-toluene Br2 1:1:0 CH2Cl2 traces traces
p-CN-toluene Br2/H2O2 1:1:1 CH2Cl2/H2O 5:1 100 95
o-CN-toluene Br2/H2O2 1:1:1 CH2Cl2/H2O 5:1 97 98
o-Cl-toluene Br2/H2O2 1:1:1 CH2Cl2/H2O 1:1 100 94
p-Cl-toluene Br2/H2O2 1:1:1 CH2Cl2/H2O 1:1 100 93
p-Me-benzoic acid Br2/H2O2 1:1:1 CH2Cl2/H2O 1:1 100 87
Et-p-Me-benzoate Br2/H2O2 1:1:1 CH2Cl2/H2O 1:1 100 91
p-NO2-toluene Br2 1:1:0 CH2Cl2 21 100
p-NO2-toluened Br2/H2O2 1:1:1 CH2Cl2 100 88
p-NO2-ethylbenzened Br2/H2O2 1:1:1 CH2Cl2 98 86
2-NO2-4-MeO-toluene Br2/H2O2 1:1:1 CH2Cl2/H2O 1:2 85 98
a Based on the converted alkylbenzene. b 28% of PhCHBr2 is formed. c alpha-Methylstyrene and alpha-methyl-beta-bromostyrenes are the main reaction products. d 36% aqueous H2O2 has been utilised.
fear fear hate hate 		 
 
 
 
    moo
(Hive Bee)
11-01-03 01:22
No 468080
       Another one
(Rated as: good read) 		    

High atomic yield bromine-less benzylic bromination
Mestres, Ramon; Palenzuela, Jesus
Green Chemistry 4(4), 314-316 (2002)
DOI:10.1039/b203055a

Abstract
A two-phase mixture (sodium bromide, aqueous hydrogen peroxide/carbon tetrachloride or chloroform) under visible light provides a simple and convenient system for benzylic bromination of toluenes. A high atomic yield for bromine atoms is attained. Substitution of the chlorinated solvents by other more environmentally benign organic solvents has been attempted and good results are obtained for methyl pivalate.
fear fear hate hate 		 
 
 
 
    Rhodium
(Chief Bee)
11-01-03 07:33
No 468126
       THF to GBL in 75% yield in 4h using H2O2/Br2     

This caught my eye:

Oxidation of Tetrahydrofuran (THF) to gamma-Butyrolactone

Ten millimoles of THF and 4 mmol of Br2 were refluxed for 1 h in a mixture of 5 mL of CH2Cl2 and 5 mL of water. Four millimoles of H2O2 was added, and the mixture was refluxed for 1 h; an additional 4 mmol of H2O2 was added, and the mixture was refluxed for 2 h.

After four hours they achieve 92% conversion and 81% yield, meaning that THF can be converted to GBL in 75% overall yield using hydrogen peroxide with catalytic bromine (which can be made in situ from any bromide salt)...

Who is going to be the first to scale this up to a usable environmentally friendly OTC GBL production procedure? 		 
 
 
 
    WeakEndChemist
(Stranger)
11-19-03 21:30
No 471887
       Understanding this interaction     

Trying desperately not to be referred to a n00b who should have use tfse, I have searched a bit in reference to what exactly is catalytic bromine.  Obviously it's formed from a bromine salt, and I've found that NaBr is fairly easy to purchase.  Being that it's called Br2 i'm assuming it's elemental bromide... however, i always figured that it's damned hard to break a salt into elemental parts because of the strong ionic bond in them.  So figuring this out on my own has been a horrific failure.  I won't lie and say i know enough about chemistry, so please pity the fool.

Thanks
Sure, I'll try some... Is it dangerous? 		 
 
 
 
    moo
(Hive Bee)
11-19-03 21:51
No 471889
       Understanding this reaction     

Trying desperately not to be referred to a n00b who should have use tfse

It would be much better to study chemistry as there are a lot of free resources, try it.

Being that it's called Br2 i'm assuming it's elemental bromide... however, i always figured that it's damned hard to break a salt into elemental parts because of the strong ionic bond in them.

It is elemental bromine, not bromide. The hydrogen peroxide is used to oxidise the bromide ions to elemental bromine, which then goes on and oxidises whatever it is used to oxidise thusly being reduced back to bromide ions, which are then available for reacting again in the same manner. That is why it is called catalytic bromine, it isn't used up in the reaction but hydrogen peroxide is.

If you want to understand these reactions you must at least read the article, I didn't include the PDF for nothing. If you do not understand what they say... well, then I guess you'll just have to study chemistry as there is no other way to be able to understand chemistry. It is much fun in the end.smile
fear fear hate hate 		 
 
 
 
    Chromic
(Synaptic Self-Mutilator)
11-19-03 22:00
No 471892
       Not me     

My problem was that the THF that one can get from pipe cement contains acetone. If you try and form Br2 and react it with "mostly pure" THF, you will get bromoacetone. The bromoacetone formed left me crying. It's highly irritating shit to deal with, even in small qty's. Post 363729 (Chromic: "bromoacetone", Chemistry Discourse)

I'd absolutely love to see someone work on this who has access to reagent grade thf... (well, I do, but I have to go thru a chem supplier--and THF isn't really watched, so, perhaps I'm just complaining) 		 
 
 
 
    Rhodium
(Chief Bee)
11-19-03 23:29
No 471906
       removing acetone from THF     

Can't you remove the acetone from the THF by washing with bisulfite, or if everything else fails, reduce the acetone to IPA and then distill the THF/IPA mixture from KOH or Mg/I2 (which should trap the IPA as its alkoxide)? 		 
 
 
 
    Chromic
(Synaptic Self-Mutilator)
11-21-03 01:23
No 472204
       Washed with bisulfite     

Yeah, I did wash with bisulfite. That didn't remove all of it... perhaps other suggestions you mentioned would have worked. Ideally I should get some pure THF to do this sort of experimentation with. 		 
 
 
 
    Chromic
(Synaptic Self-Mutilator)
11-27-03 11:09
No 473493
       Some more questions     

Moo, in the Deno paper that you dug up, J. Am. Chem. Soc.; 1967; 89(14); 3550-3554, mentioned in Post 308130 (moo: "THF oxidations", Novel Discourse) I noticed that they use 4x equivilants of Br2 and conduct this experiment cold and in the dark.

If I've got this right, the paper mentioned in this post uses 1.2 eq Br2 (.4eq added as Br2 and .8eq generated catalytically as in H2O2 + 2 Br- + 2 H+ -> Br2 + 2 H2O) and conducts it at reflux with no mention of protecting from light. This is just strange. 1.2eq versus 4eq? They also change the solvent system from just water (as in the Deno paper) to a mix of DCM and water. Can anyone think of any reasons for changing the conditions so much?!?

Of course, there's also the great Tetrahedron; 2000 56; 1905-1910 ref as well that uses bromate... they talk about over-oxidizing the THF and forming small amounts of succinic acid... although they do isolate most of the product, 75% yield, thru atmospheric distillation.

Also, can you guys see anywhere if the 75% yield in this paper is an isolatable yield, or is it a GCMS yield? (like the GABA->GHB/GBL is a 100% yield by GCMS--but of that only 75% can be isolated) They just say that "the mixture was analyzed"--which doesn't say much.

P.S. why is there three bromine/THF refs and one H2O2/THF refs on the hive and no one but me as reported results on them? Am I just unaware of other people working on these routes? 		 
 
 
 
    moo
(Hive Bee)
11-27-03 18:34
No 473540
       THF / GBL / Br2 / H2O2
(Rated as: excellent) 		    

Moo, in the Deno paper that you dug up, J. Am. Chem. Soc.; 1967; 89(14); 3550-3554, mentioned in moo: "THF oxidations" (Novel Discourse) I noticed that they use 4x equivilants of Br2 and conduct this experiment cold and in the dark.

In that ref they tried the ratios of THF:Br2 1:5, 4:1 and about 5:1. The focus of the article was on studying the kinetics and mechanism of this reaction, so I guess they weren't so interested in seeing if the reaction works with stoichiometric ratios of the reactants. In that post I say that they did the reaction in dark to avoid free-radical bromination -- this is a claim I must take back not only because of the article posted in this thread, but because of the following quote from the Deno article:

It was evident from qualitative observations that irradiation, even by simple sunlamps, greatly increased the rate of disappearance of Br2. Where the irradiated reaction gives the same products as the dark reaction, it would presumably be preferable from a synthetic viewpoint. However, in the one case investigated with care, benzyl isopropyl ether, the irradiated reaction gave different products. In retrospect we regret that we did not examine the light-catalyzed reaction more extensively.



It might be that this reaction can proceed both by ionic and free-radical mechanisms but evidently it doesn't matter in practice.

If I've got this right, the paper mentioned in this post uses 1.2 eq Br2 (.4eq added as Br2 and .8eq generated catalytically as in H2O2 + 2 Br- + 2 H+ -> Br2 + 2 H2O) and conducts it at reflux with no mention of protecting from light. This is just strange. 1.2eq versus 4eq? They also change the solvent system from just water (as in the Deno paper) to a mix of DCM and water. Can anyone think of any reasons for changing the conditions so much?!?

In the table 13 they say "Conversion based on oxidant", so not all THF gets oxidised in that example. The other example of an ether oxidation uses 2 equivalents of hydrogen peroxide in addition to 0.1 equivalents of elemental bromine.

Why the two-phase system? That is one of the key features of their article, the fact that the two-phase system affects certain reactions positively and eliminates unwanted side reactions, so they go on and try the same system with other substrates. In other refs DCM is not needed at all. It could be that this reaction is not so fickle and various reaction conditions can lead to good results.

Also, can you guys see anywhere if the 75% yield in this paper is an isolatable yield, or is it a GCMS yield? (like the GABA->GHB/GBL is a 100% yield by GCMS--but of that only 75% can be isolated) They just say that "the mixture was analyzed"--which doesn't say much

The 73% yield is the isolated yield, GC says 80%. ../rhodium/pdf /thf2gbl.pdf

P.S. why is there three bromine/THF refs and one H2O2/THF refs on the hive and no one but me as reported results on them? Am I just unaware of other people working on these routes?

I think there have been mentions of the H2O2/Fe(II) method being horribly messy but no actual results. It might be that as the doses of GHB are so high that a good GBL method is characterised by good volume efficiency, and there is no simple worked-out volume-optimised method, nobody has wanted to start messing with the scary peroxide-forming THF and the possibility of failure. By the way, there are five Br/THF refs, two of them mentioned in Post 381459 (moo: "THF -> GBL patents etc.", Methods Discourse). It is possible to use chlorine too. Maybe a possibility for a H2O2/HCl method? Or an electrolytic cell with NaCl as the electrolyte with sulfuric or hydrochloric acid added so that the pH is 1 as recommended (Post 243610 (foxy2: "Re: Easy Oxidation of THF to GBL", Novel Discourse))?

I still haven't found out if lead oxide (PbO2 aka lead peroxide in older literature) is suitable for an anode in oxidation of halogen ions. Both graphite and platinum are used for this purpose.

fear fear hate hate 		 
 
 
 
    Chromic
(Synaptic Self-Mutilator)
11-29-03 01:56
No 473746
       Uhm     

Also, can you guys see anywhere if the 75% yield in this paper is an isolatable yield, or is it a GCMS yield?

Moo, I meant for the paper in this thread. Not for the bromate ref on Rhodium.

I'm pretty sure I'll attempt this chemistry if I have enough time. I'd be aiming towards more like 100ml THF, small amount NaBr (10g?), small amount of acid, (perhaps a small amount of DCM, ie 100ml) then slowly adding  like ~150g 35% H2O2 (ie about 1.2eq and keeping at reflux if done in DCM). The volumes in that case would be much more reasonable. Thoughts? The theory would be around 100ml of GBL, hopefully one could recover half that. Those volumes would be quite competitive with GBL produced via GABA diazotiation. 		 
 
 
 
    moo
(Hive Bee)
11-30-03 01:21
No 473862
       Oh, of course! :-D I think it is a GC/MS ...     

Oh, of course! laugh I think it is a GC/MS yield, as it seems the yields for the other reactions are always analyzed that way and never isolated.
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