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JJay
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AvBayer's suggestion of methyl tosylate has considerable appeal. It looks like a fun and interesting chemical to play with, and it's not impractical.
Preparation of dimethyl sulfate is not a great experiment for someone who doesn't have years of experience snuffing out fires and dealing with deadly
gas leaks. Even some of the greatest amateur chemists think it is too dangerous to attempt. I'm going to have to work out an appropriate fume hood...
my biggest concern is containing possible spills....
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Pumukli
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Tosylates are good methylating agents IF you can make/buy the chlorides. Unfortunately there is no simple route to the methylester from the free acid.
If there was, well, it would really help the amateurs. They would be easily recyclable too.
By the way, you can go "fancy" with the sulfonates: electron withdrawing groups in the p-position of their benzene ring makes even better alkylating
agents. Once I saw a comparison of reaction rates of various substituted sulfonates and there was a more than tenfold increase of it from p-methyl to
p-chloro (or p-nitro?).
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Sigmatropic
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I remember some of the higher tosylates can be made by using a trialkyl borate (specific example was with tosylic acid and tributyl borate). Perhaps
the methyl compound can be made that way but alot changes. Most importantly the boiling points of the borate, the alcohol and their possible
azeotropes with water. Hence the way in which you can force these reaction changes dramatically. I will try to find references tomorrow.
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Loptr
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Quote: Originally posted by Pumukli  | Tosylates are good methylating agents IF you can make/buy the chlorides. Unfortunately there is no simple route to the methylester from the free acid.
If there was, well, it would really help the amateurs. They would be easily recyclable too.
By the way, you can go "fancy" with the sulfonates: electron withdrawing groups in the p-position of their benzene ring makes even better alkylating
agents. Once I saw a comparison of reaction rates of various substituted sulfonates and there was a more than tenfold increase of it from p-methyl to
p-chloro (or p-nitro?). |
Cobalt(II) catalyzed tosylation of alcohols with p-toluenesulfonic acid
Subbarayan Velusamy, J. S. Kiran Kumar and T. Punniyamurthy*
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
Received 23 July 2003; revised 7 October 2003; accepted 17 October 2003
Attachment: Cobalt(II) catalyzed tosylation of alcohols with p-toluenesulfonic acid.pdf (238kB)
This file has been downloaded 425 times
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Alcohol (3 mmol), p-TsOH (3 mmol) and CoCl2*6H2O (5 mol %) were dissolved in ClCH2CH2Cl (10 mL) and the solution was stirred under reflux (ca. 80 C)
for the appropriate time (see Table 2). The reaction mixture was then allowed to cool to ambient temperature and diethyl ether (50 mL) was added. The
catalyst was removed by filtration and the filtrate was washed successively with saturated NaHCO3 solution (3 · 10 mL), brine (2 · 10 mL), and water
(1 · 10 mL). Drying (Na2SO4) and evaporation of the solvent on a rotary evaporator afforded a residue, which was passed through a short pad of silica
gel using a mixture of ethyl acetate and hexane as eluent to afford the analytically pure tosylate.
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[Edited on 14-9-2018 by Loptr]
"Question everything generally thought to be obvious." - Dieter Rams
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AJKOER
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Per a source, try following the general method (regrettably reversible) of obtaining methyl sulphate from the action of concentrated sulphuric acid
acting on CH3OH but use methanol vapors at low temperature (like -40 C, see http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.530...). To quote:
"The uptake of gas-phase methanol by liquid sulfuric acid has been investigated over the composition range of 40 - 85 wt % H2S04 and between the
temperatures of 210 - 235 K.
.....
While reversible uptake was the primary mechanism at low acid concentrations, irreversible reaction between methanol and sulfuric acid at low
temperatures, forming methyl hydrogen sulfate and dimethylsulfate, was observed at all concentrations. Above 65 wt % H2S04, more than 90 % of uptake
was found to be reactive."
My summary reaction:
CH3OH (g) + H2SO4 (l) --(-40 C)--> CH3HSO4 (l) + H2O (s)
CH3HSO4 (l) + CH3OH (l) --> (CH3)2SO4 (l) + H2O (s) (See Eq 8 )
----------------------------------------------------------------------------
Here is also an experimental photolysis path (to be tested/verified) for those restrained to more ambient temperature ranges. It employs methanol
under UV photolysis resulting in the formation of the methyl radical and the hydroxyl radical. As such, I would recommend trying to obtain methyl
sulphate from the action of concentrated persulphuric acid acting on methanol, in the further presence of UV light. Expected reactions:
CH3OH + hv --> •CH3 + •OH (and other products, see http://chemistry.emory.edu/faculty/widicusweaver/photolysis.... )
H2S2O8 = H+ + HS2O8-
HS2O8- = H+ + S2O8(2-)
S2O8(2-) + hv --> •SO4- + •SO4- (see, for example, https://www.sciencedirect.com/science/article/pii/S004565350... )
H+ + •SO4- = •HSO4 (pKa < 0)
•CH3 + •HSO4 --> CH3HSO4
CH3HSO4 + CH3OH --> (CH3)2SO4 + H2O
CH3HSO4 + H2O = CH3OH + H2SO4
.....
Hopefully by restricting the presence of water, the last reaction will be limited. Some unwanted reactions, likely detracting from yield, include:
•OH + •HSO4 --> H2O + SO4(2-)
•OH + SO4(2-) = OH- + •SO4-
OH- + H+ = H2O
---------------------------------------
Here is also a photolysis path to methyl iodide. Starting with iodide (from say HI) , the hydroxyl radical forms the monatomic iodine radical as does
the direct action of light on iodide. The methyl and the iodine radical could then theoretically combine creating methyl iodide. Reactions including
some other products:
HI = H+ + I-
CH3OH + hv --> •CH3 + •OH
I- + hv --> •I + e-
H+ + e- = •H
I- + •OH --> •I + OH-
•H + •OH --> H2O + photon
•H + •I --> HI
•CH3 + •I --> CH3I
•CH3 + •H --> CH4
……..
and other products.
[Edited on 15-9-2018 by AJKOER]
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clearly_not_atara
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Loptr wins the thread. That is incredible. I think you'll want an excess of methanol to compensate for losses. Or maybe you can just perform the rxn
in methanol?
| Quote: | | Once I saw a comparison of reaction rates of various substituted sulfonates and there was a more than tenfold increase of it from p-methyl to p-chloro
(or p-nitro?). |
Para-bromobenzenesulfonates, affectionately "brosylates", are the most common IIRC.
[Edited on 15-9-2018 by clearly_not_atara]
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Loptr
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Alright, it now looks like dimethyl sulfate is now available in the USA.
I placed an order a few days ago and am still waiting for a shipment notification. And it's cheap, too! Cost me $39.62 in total for 500ml, and that's
including shipping.
To be honest, I will be surprised if it arrives.
[Edited on 19-4-2019 by Loptr]
"Question everything generally thought to be obvious." - Dieter Rams
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