SnCl2 reduction of Nitro

[Sky]

How does The SnCl2 reduction Nitro Toluene Go? I can't find any references. most of the reduction use Tin or Iron Powder and HCL acid. I read in a Organic Chem. Book were it referred to 1.SnCl2+H3O+ 2. H20+OH- but it did not go into details.

[Cheapskate]

I've never tried the Tin reduction.  I think I have a write up on one that Piglet sent me.  I'll take a look.  The reason I never got to it was the cost of Tin, it's way higher than zinc or aluminum.  Aluminum didn't work, zinc did, but was as much trouble, mess and stink as the iron one.  I remember having a heck of a time with zinc oxide that somehow crept into the procedure.

[Sky]

I made Some SnCl2 and it was a salt like crystals not a metallic powder very hydroscopic. It may be a Cleaner reaction.

[Cheapskate]

This is what Piglet sent me…..Actually it looks pretty darn good.

                              Sn/HCl
Ph.NO2 + 6[h] -------------------? Ph.Nh2  +  2H2O

Into a 500ml RB flask equipped with a reflux condenser, place 25g (21ml, 0.25mol) of nitro benzene & 45g of granular tin.  Measure out 100ml Conc.HCl.  Pour about 15ml down the condenser and shake the flask steadily.  The mixture becomes warm & before long the reaction should be quite vigorous.   If it boils very vigorously, moderate the reaction by immersing the flask in cold water.  When the initial reaction slackens, add further 15ml logs, following the above workup, until all the HCl has been added.  Heat the mixture on a boiling water bath for 30-60 minutes.  During this reduction, particularly during the cooling, aniline chlorostannate may separate as a white/yellow crystalline complex.

Cool the flask to RT & gradually add 75g NaOH in 125ml dH2O;  If the mixture boils, cool again.  The hydroxide of tin, which is first precipitated, should all dissolve & the solution should be strongly alkali.

Equip the flask for a steam distillation & pass steam into the warm mixture until, after the distillate has ceased to pass over as a turbid liquid, a further 120ml of clear liquid is collected.  Since aniline is 3% water soluble, it must be salted out with NaCl (about 20g per 100ml liquid).  Transfer the distillate, saturated with NaCL, into a sep. funnel and extract twice with 40ml portions of ether.  Distill off ether & distill fraction 180-184C.  Yield, 18g, 97%

Now in going for toluidine, it might separate into a separate liquid layer that can just be separated.

Thoughts?

[Sky]

I was Thinking the same thing. I will work on it.

[Sky]

Cheapskate I tried the Tin reduction it was about the same as the Iron reduction Stunk to high heaven. The part were you salt out the product with NaCl was an inprovement.

[Cheapskate]

Details!!  Did you actually have to do a steam distillation?  How hard was the clean up afterwards?  It takes about 3 days to get the glassware clean after the iron reduction.  Did the liquids separate?  You know the kind of stuff I wanna know.

I don't think there is any way to get rid of the smell of the nitrotoluene.  This stuff smells up the entire neighborhood, but the smell can be reduced with a vacuum pump leading to the drain so it goes into the sewer. 

By the way, to separate the isomers of nitrotoluene:  put the stuff in a bottle and seal (to keep stink in) and place in  the freezer until it all solidifies.  Then take it out and let it come to room temperature.  The o isomer will return to liquid and the others will tend to stay semi-solid.  It can be vacuum filtered.  Do this twice and you have close to pure o isomer.  Amazing how much you lose, but it would have been lost anyway. 

I'm still working on the anthranilic from phthalimide.  I've gotten it to work, but the yield is around 20% and unreliable.  Never did get Methacosmic's method to work, even after he contacted me by mail.  Phthalimide is relatively cheap, US$25 per kg is a normal price.

What did you wind up paying for tin?

[Sky]

I did have to Steam Distill But after the addition of base water I super saturated it with NaCl which caused the Toluidine to seperate beautifully. The Clean up was more of a red mess than a Black one But Just as Bad. The Tin was free 

[Sky]

I did have to Steam Distill But after the addition of base water I super saturated it with NaCl which caused the Toluidine to seperate beautifully. The Clean up was more of a red mess than a Black one But Just as Bad. The Tin was free 

[Cheapskate]

Damn, there's got to be a cleaner way to do this.  I can live with the steam distillation and the smell, but taking a couple of days to clean up the glassware sucks.  By the way, how did you stir this stuff?  I used a variable speed dremmel tool on the iron one, rusted the chuck solid!  Tin can probably be mag stirred.  Also, it would be nice to get a higher volume out of this, 15grams is awfully small.

[Sky]

I was thinking you could use an aquarium pump to stir up the mix. I Don't Know if the extra oxygen would mess up the reduction or not?

[Cheapskate]

I once tried using the output side of a vacuum pump to stir the mix on an iron reduction.  It didn't seem to cause a problem with the reduction, but the splash of caustic solution was a problem.  There was also a HUGE increase in smell since the bubbles were carrying the smell right out of the apparatus.  The flowing air seemed to cool the solution a lot and extra heat had to be added.

Do you know of a commercial source of tin (as opposed to a chemical supplier source)?

[foxy2]

This appears to bee a nifty way to reduce o-nitrotoluene to o-toluidine!

Selective reduction of aromatic nitro compounds with stannous chloride in non acidic and non aqueous medium
Tetrahedron Letters, Volume 25, Issue 8, 1984, Pages 839-842
F. D. Bellamy, and K. Ou

Abstract
Aromatic nitro compounds are readily reduced by SnCl2*2H2O in alcohol or ethyl acetate or by anhydrous SnCl2 in alcohol where other reducible or acid sensitive groups such as aldehyde, ketone, ester, cyano, halogen and O-benzyl remain unaffected.


In our search for a mild, selective, inexpensive and general method for this transformation, we found that either SnCl2*2H20 in alcohol or ethyl acetate, or anhydrous SnCl2 in alcohol work very efficiently (5). A wide variety of substituted nitrobenzenes had been selectively reduced in almost quantitative yields using this simple procedure (see table). Under the conditions used, other reducible or acid sensitive groups are recovered unchanged. The table also shows that the yields of substituted anilines are not affected by the nature or the position of the aromatic substituents on the corresponding nitrobenzenes. The yields obtained in the presence of groups such as aldehyde, O-acetate and 0-benzyl are particularly noteworthy.

Table: Reduction Results for various Nitrobenzene's
------------------------------------------------------------
Substituents on nitrobenzene; Yield(%)
------------------------------------------------------------
p-Cl; 96%
p-Cl,m-CN; 98%
p-COOEt; 97%
p-OCH3; 97%
p-Cl,m-COOEt; 95%
p-CHO; 96%
p-COOH; 94%
p-OH; 91%
p-OCOCH3; 92%
p-OCH3,o-CN; 99%
m-CH3,o-COOH; 99%
p-PhCH2O; 91%
------------------------------------------------------------


Procedure
A typical experimental procedure is illustrated below for the reduction of p-nitrobenzoic acid: a mixture (6) of 1.67 g (0.01 mole) of p-nitrobenzoic acid and 11.275 g (0.05 mole) of SnCl2*2H20 (7) in 20 ml of absolute ethanol is heated at 70°C under nitrogen. After 30 mn the starting material has disappeared and the solution is allowed
to cool down and then poured into ice. The pH is made slightly basic (pH 7-8) by addition of 5 % aqueous sodium bicarbonate ( before being extracted with ethyl acetate. The organic phase is thorougly washed with brine, treated with charcoal and dried over sodium sulphate. Evaporation of the solvent leaves 1.5 g (94,5 %) of p-aminobenzoic acid, which gives one spot on tlc and melts over 300C.


We feel that the mildness and the selectivity of this method which works in nonaqueous conditions together with the ease of the treatment and the purity of the products obtained should largely extend the scope of the use of stannous chloride which is a safe and inexpensive reagent.


6. SnCl2*2H20 and anhydrous SnCl2 are both insoluble either in ethanol or in ethyl acetate as already noted by J.R. Sampey, J. Am. Chem. Sot., 2, 88 (1930).

7. SnCl2*2H20 or anhydrous SnCl2 can be used indifferently. When SnCl2*2H20 may be utilized in ethanol (absolute or not) or in ethyl acetate or in a mixture of these solvents, the presence of ethanol is necessary for the reduction with anhydrous SnCl2 to work.

8. 5 % aqueous sodium bicarbonate may be replaced by solid sodium bicarbonate, or aqueous or solid NaOH Without affecting the yield noticeably.
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[foxy2]

Conformationally defined adrenergic agents. 8. Synthesis of conformationally defined analogs of norfenfluramine. A highly stereospecific synthesis of amines from alcohols in the benzobicyclo[2.2.1]heptene system
G.L. Grunewald and al.,
J. Org. Chem., 48, 2321 (1983)


Procedure: 2-Bromo-4-amino-6-(trifluoromethyl)acetanilide (20).
To a slurry of 520 g (2.3 mol) of SnCl*2H20 in 940 mL of EtOH was added 103 g (315 mmol) of 2-Bromo-4-nitro-6-( trifluoromethyl)acetanilide(19) with stirring. The mixture was refluxed for 0.5 h, stirred at room temperature for 13 h, and then basified to pH 11 with 2 N ethanolic NaOH. The slurry was filtered and the solid SnO2 washed with ether. The aqueous layer was separated and extracted with ether. The combined ethereal extracts were dried (MgSO4, and the ether was evaporated to yield 80.5 g (86%) of 20 as a yellow powder, mp 202-205C. Recrystallization from MeOH(2X) afforded colorless needles: mp 211.5-213C

Those who give up essential liberties for temporary safety deserve neither liberty nor safety