Isopropyl Nitrate Purification

My father's crazy about model plane diesel engines, and has been wanting
some isopropyl nitrate to use as a 'cetane booster'. The published
synthesis methods (using an alkyl halide, or a continuous distillation)
weren't practical for me, so I've tried a direct nitration (using *very*
small quantities of reactants), eventually with some success. The
nitration employs a mixture of nitric acid, isopropyl alcohol and urea
nitrate, in close to stoichiometic amounts.

My problem is the purification of the volatile liquid the reaction
produces. This liquid is a transparent yellow, whereas some MSDSs for
IPN list it as colourless. I've tried extracting with water, followed
by saturated NaHCO3 solution, but the colour remains (although the
NaHCO3 solution effervesces and turns an opague red). I don't have the
equipment to distil IPN, and considering its flash point and volatility
I don't want to try. I haven't tried activated carbon, and haven't
measured the boiling point of the unpurified liquid yet.

Do you have any suggestions on purifying the IPN? I can post details of
my method if it would help. Please, no flames about trying to directly
nitrate a secondary alcohol.

As a side question, any ideas on the nature of the red colour formed
when extracting with NaHCO3? AFAIK, the only major side product of the
reaction should be acetone.


Thanks in advance,

Mark Pinese

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Mark Pinese

"Mark Pinese" <[Only registered users see links. ].edu.au> wrote in message
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In the separation funnel repeat the NaHCO3 treatments until there's
no longer any bubbles. Then wash a few times with H2O to pH 7-7.5
Then activated carbon is most likely your ticket, if the yellow impurity
is of an aromatic nature. If the discoloration stems from traces of NOx
then I'd try FeSO4, which IIRC, forms an FeSO4(NO) complex and
removes the NO + NO2.
Good luck and caution, dude.
You've got only 2 good eyes and hands! Careful!


No, no, you'll get all kinds of condensation products, depending on
reaction conditions, including isophoron and mesitylene and its colored
nitro compounds.

Mark Pinese <mark.pinese@spamstudent.unsw.edu.au> wrote:

Mark, first off, are you sure it's "isopropyl nitrate" (a nitrate
ester) that you want and not 2-nitropropane? These are two different
beasts, as you probably know.


Off the cuff I'd say that greater than 2/3 of all organic reactions
produce some yellow color. The identity of the colorant is usually
not well defined, nor is a precise method for its removal. The color
is typically caused by a very small amount of highly colored material,
meaning that a pronounced yellow cast may not indicate low purity. In
particular, for use in model engines, a small amount of "yellow color"
probably won't hurt anything. But traces of remaining acid could do
plenty of damage, so take hanson's advice and make sure to wash your
product until all of the acid is removed.

If you really want to get colorless material, there is probably no
better way than distillation. With low molecular weight nitrate
esters, however, this can be a perilous proposition. Be very, very
careful. And don't let the dep't of homeland defense find out what
you're doing...

Steve Turner

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Steve Turner wrote:


Absolutely. I'm after the nitric acid ester, (CH3)2CHONO2 (although it
seems the nitrite, (CH3)2CHONO, will work as well -- another 'cetane
booster' in use is amyl nitrite. I figured IPN will cause fewer legal
difficulties. ).



Yes, I don't think I'll be very liked around here if the IPN transforms
an engine into a pile of corroded goo.


LOL. Distillation is definitely out, although I might do a BP this
afternoon with a micro method I found in Vogel.


Thanks for your help.

Mark Pinese

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hanson wrote:


Wouldn't the NaHCO3 take care of any NOx lying about, converting it to
the respective sodium nitrate or nitrite?



Would these be very abundant? I'm using equal volumes of 63.8% HNO3 and
99.5% IPA, with some urea nitrate to scavenge any HONO. The maximum
temperature reached is usually around 33C (for a few seconds), and the
reaction is kept below 25C for most of the time (~ 10 mins total).


Mark Pinese

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"Mark Pinese" <mark.pinese@spamstudent.unsw.edu.au> wrote in message
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I think NaHCO3 will only take care of the N2O3 ----> HNO2 system
and then only to the pH equilibrium between HCO3-/NO2- system.
Bicarb will not do anything to the uncharged NO and NO2 or N2O4.
With them you will also have an equlibribrum. Dunno details. BUT:
I suggest that once you have the reaction done, add plenty of NaNO3
(Sod. Nitrate) to split and salt-out the organic and water phases from
each other. Then you MAY have a relatively pure organic phase.

Dunno, how abundant these Actone condensates will be.
The longer and higher t and T are the more you will get.

I'd use not only "some" Urea*HNO3, I would saturate both the IPA and
the HNO3 conc. separately with it first and then mix the 2 slowly
in an **ice bath** under *gentle* shaking. NO stirring. The shit you
are cooking here has very unpredictable tendencies, and if things
just go according to Murphy's law, and they will, it'll certainly blow up
in your face. Don't do neither the classical mistake of making "certain"
by doing it with a few ml first to make "sure", and when nothing happens
assume that a 10 to 100 fold scale up will be ok. It will not be ok!
It will be worse and more dangerous and less predictable.

I can't tell you whether you should dribble IPA into HNO3 or the other
way around to get better yields, only experiment will show, BUT your
33C and even the 25C looks to me like then temp for a bomb!
That is way too hot! DON'T DO THAT. You'll be blowing your ass to pieces!
*** All alcohol nitrations are carried out close to zero degree Celsius.***

The "safest" way for you to do it is to find the "receipe" in the literature.
of how "they" made Me, Et, Bu and Amyl nitrate and then adjust
the parameters accordingly, as IPA lays in the middle.

hanson wrote:


I've done this a few times now (7 successful runs, no runaways using the
latest method), with a total reaction volume not exceeding 10mL. I
don't intend to scale the synthesis up at all considering the cooling
difficulties posed. As only a few percent IPN is required in the fuel,
I'm only after a very small scale prep. If you want to criticise my
method, please ask me to post it in detail first; what I gave before was
only a summary of reaction conditions.


That was the first thing I tried, with no product formed. I am unsure
of the chemistry, but even when left for a couple of hours, no reaction
seems to occur until the solution is initially warmed to ~28C.


The literature I've consulted give two methods for the preparation of
IPN: the reaction of an isopropyl halide with an inorganic nitrate, and
a continuous industrial method in which urea, HNO3 and IPA are
continuously added at > 100C while IPN is distilled off. Most sources
state that the direct nitration of IPA is impractical / impossible, due
to the ease with which it is oxidised to acetone. In this regard, the
synthesis of IPN from IPA (a secondary alcohol) is completely different
from the nitration of the alcohols you gave, which are all primary.
However, it seems that with very careful regulation of temperature and
the presence of urea, the amount of oxidation can be minimised.


Mark Pinese

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Mark Pinese <[Only registered users see links. ].edu.au> wrote:


For what it's worth, Davis reports in his landmark book on explosives
that nitrations of glycerine are (or were) carried out at a max. of 22
C in Britain and 25 C in the U.S. Of course, glyceryl trinitrate is
much more sensitive than iPr-ONO2. In my opinion, you're probably
okay at RT as long as you maintain it there. If you see red fumes,
you're oxidizing and in danger of thermal runaway. I'd keep a large
bowl of icewater handy to quench the whole thing if it threatens to
get away from you.

The CRC lists the bp of iPr-ONO2 as 100-101 (no pressure given,
assumed to be atmospheric).

Steve Turner

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Steve Turner wrote:


I checked COPAE (I assume that's the Davis you're referring to) before
even thinking about making IPN -- a sensitive explosive is something
I'll never try to mess with again (iodine and NH4OH 'educated' me back
in primary school ). IIRC, COPAE had a section on IPN, but it wasn't
useful.

Early-on, I had two runaways; fortunately they were easy to recognise.
35C is definitely stretching things, and by 40C the solution is red,
with red fumes above it. A few seconds later it will boil violently --
the thermometer when recovered showed 80C, so I assume the reaction was
stopped by the boiling off of any IPA remaining. 25C works for me as
being easy to maintain and (so far!) safe.

I'll try your extraction reccommendations on Monday and let the group
know how things went. The major objective is to remove any nitric acid
traces -- diesel fuel contains kerosene.


Mark Pinese

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