Sciencemadness Discussion Board

Preparation of a "spectacular" thermochromic solid

pantone159 - 29-12-2008 at 17:43

I just saw this interesting letter in the new Journal of Chemical Education, and I thought I would mention it to the board.

http://jchemed.chem.wisc.edu/Journal/Issues/2009/Jan/abs30.h...

A material, (Me2NH2)2NiCl4, is prepared that shows interesting changes in color with temperature. At room temp the solid is raspberry red, after heating to 110 C is changes to deep blue, then after cooling it changes to a metastable yellow form. After some weeks, the material reverts to the red form.

It is prepared by heating stoichiometric amounts of well mixed dimethylamine HCl and anhydrous NiCl2 in an ampule, which is then sealed.


[Edited on 29-12-2008 by pantone159]

Attachment: JCE2009p0030.pdf (147kB)
This file has been downloaded 900 times

pantone159 - 29-12-2008 at 17:46

Also see:

Attachment: JCE2009p0030W.pdf (59kB)
This file has been downloaded 839 times

kclo4 - 29-12-2008 at 19:41

Very Interesting! Thanks for posting that. The precursor chemicals look easy to make.
the colors are very vivid!

octave - 1-1-2009 at 21:15

Is there any more in depth details of this synthesis other than "mix them together and heat"?

pantone159 - 1-1-2009 at 21:29

Quote:
Originally posted by octave
Is there any more in depth details of this synthesis other than "mix them together and heat"?


From the second attached pdf...
Quote:

Synthesis
Dimethylammonium chloride was prepared from concentrated aqueous solutions of
dimethyl amine (DMA) and of hydrochloric acid (2 drops of the amine were added in
excess). The solution of the salt obtained was evaporated on a hot stage, till white solid mass
is left. The solid (dimethylammonium chloride, i.e. DMAC) was thoroughly mixed with a
glass rod, till all of the water is gone. The salt is hygroscopic and should be kept in a
dessicator with P2O5 if not used immediately. Alternatively, if an excess of the salt is
prepared, it may be kept in sealed ampoule too (see below).
Stoichiometric quantities of dimethylammonium chloride and anhydrous nickel(II)
chloride (a total mass of 0.5–2 g) are quickly transferred in a warm ampoule (≈ 50 °C)
prepared from a standard test-tube (160 mm × 16 mm, see below) and the ampoule is sealed
immediately. The solids are thoroughly shaken and then the mixture is heated, till a uniform
deep blue color appears. After this, the ampoule with the sealed-in thermochromic substance
is ready for use.
Properties of the Synthesized Complex
The synthesis was performed a number of times, varying the reactant ratio by some
20 % (i.e. taking each component to be in an excess of up to 20 % with respect to the ideal
stoichiometric composition of NiCl2 to DMAC of 1 : 2). The above variations always resulted
in a product with more or less the same properties (i.e. showing double thermochromism).
However, it seems that some microscopic impurities present in the DMA are responsible for
variations in the period of the phase transition from yellow to the red form. Thus, this period
may be as short as 24 h or as long as a month. We were unable to reveal the nature of these
impurities that obviously have strong (catalytic?) influence over the phase transition of
interest. Anyway, in all studied samples the yellow form eventually turns into the red one. It
also seems that for the first color transition from yellow to red the time period is the longest
one, and the subsequent transformation require shorter periods (possibly due to traces of the
red form that are present).
Preparation and Sealing of the Ampoules
The ampoules are prepared from standard test tubes (160 mm × 16 mm), by heating
the test tube about 6 cm below the test tube mouth. The test tube is heated, first gently, then
gradually stronger (using a Bunsen burner) till the glass softens, while rotating the tube about
its axis. When the glass is soft enough, the tube is quickly stretched, giving the desired
ampoule. This procedure needs some practice, but after trying several tubes the result is quite
satisfactory.
The anhidrous powders (i.e. NiCl2 and dimethylammonium chloride) are quickly
transferred (using a small and dry funnel) into the above-prepared ampoule, and after that the
ampoule is immediately sealed by strongly heating its neck with the burner

woelen - 2-1-2009 at 05:11

Wow, this looks really interesting. Sadly I have no simple dimethylamine salts or an aqueous solution of this. NiCl2 is not a problem for me.

I do have dimethylamine borane complex. Could this in some way be used to make such a complex?

garage chemist - 2-1-2009 at 05:39

Dimethylamine can be prepared easily by boiling dimethylformamide with aqueous NaOH. Dimethylamine escapes as a gas and can be dissolved in water.
Buying dimethylamine is unnecessarily expensive and suspicious, as the substance is subject to chemical weapon control legislation, similar to e.g. PCl3.
Dimethylamine-borane is way too valuable to make dimethylamine out of it, get DMF instead.

benzylchloride1 - 2-1-2009 at 13:33

Take a look at page 416 of the 3rd edition of Vogels Practical Organic chemistry. There is a procedure for synthesizing dimethylamine hydrochloride from formaldehyde and ammonium chloride, this procedure produces 120g enough for hundreds of small sacle experiments. Minimal equipment is required; just a distillation set up and dessicator. This book can be downloaded from the sciencemadness library.
Here's the Procedure:

111,117. METHYLAMINE HYDROCHLORIDE (from Formalin)
Place 250 g. of ammonium chloride and 500 g. of technical formaldehyde
solution (formalin, 35-40 per cent, formaldehyde) in a 1-litre
distilling flask : insert a thermometer dipping well into the liquid and
attach a condenser for downward distillation. Heat the flask on a wire
gauze or in an air bath slowly until the temperature reaches 104° and
maintain the temperature at this point until no more distillate is collected
(4-5 hours) (1). Cool the contents of the flask rapidly to room temperature
and filter off the ammonium chloride (ca. 62 g.) which separates
rapidly at the pump. Concentrate the filtrate to one half of the original
volume on a water bath, when more ammonium chloride (ca. 19 g.) will
crystallise out on cooling to room temperature. After filtration at the
pump, evaporate on a water bath until a crystalline scum forms on the
surface of the hot solution. Allow to cool and filter off the methylamine
hydrochloride (about 96 g.) (2). Concentrate again on a water bath and
thus obtain a second crop (about 18 g.) of methylamine hydrochloride.
Evaporate the mother liquor as far as possible on a water bath and leave
it in a vacuum desiccator over sodium hydroxide pellets for 24 hours;
digest the semi-solid residue with chloroform (to remove the dimethylamine
hydrochloride), filter off (2) the methylamine hydrochloride (about
20 g.) at the pump and wash it with a little chloroform. [Upon concentrating
the chloroform solution to about half the original bulk, about
27 g. of dimethylamine hydrochloride may be obtained : the mother
liquor should be discarded.] Purify the crude methylamine hydrochloride
by placing it together with 250 ml. of absolute alcohol in a 500 ml.
round-bottomed flask fitted with a reflux condenser carrying a cotton
wool (or calcium chloride) guard tube. Heat the mixture to boiling for
about half an hour, allow the undissolved material to settle and decant
the clear solution. Cool the solution when pure methylamine hydrochloride
will separate : filter (2) and use the filtrate for another extraction.
Four or five extractions are required to extract all the methylamine
hydrochloride. The yield of recrystallised material is about 100 g.
Notes.
(1) The distillate weighs about 110 g. and contains methyl formate and methylal.
If it is placed in a flask provided with a reflux condenser and a solution of 25 g. of
sodium hydroxide in 40 ml. of water is added, the methyl formate is hydrolysed to
sodium formate and the methylal separates on the surface. The latter may be
removed, dried with anhydrous calcium chloride and distilled : about 30 g. of
methylal, b.p. 37-42°, are obtained. If the aqueous layer is evaporated to dryness,
about 25 g. of sodium formate are isolated.
(2) The best method of drying the precipitate of methylamine hydrochloride is
by centrifuging ; the compound is hygroscopic.
111.118, D1METHYLAMINE HYDROCHLORIDE
Proceed as in the preparation of methylamine hydrochloride (previous
Section) using 200 g. of ammonium chloride and 400 g. of formalin, and
heat the mixture at 104° until no more liquid distils. Cool to room
temperature and filter off the ammonium chloride (ca. 50 g.) : add 300 g.
of formalin to the filtrate, return the solution to the distilling flask, heat
until the temperature reaches 115° and maintain it as nearly as possible
at this temperature until no more liquid passes over (about 3-4 hours).
Concentrate the residue in the distilling flask on a water bath until a
scum appears on the surface of the hot liquid. Cool to room temperature
and filter off the solid (ca. 32 g.; impure methylamine hydrochloride
containing about 25 per cent, of ammonium chloride). Pour back the
filtrate into the distilling flask and heat to 120° until a sample of the
liquid, on cooling, becomes semi-solid. Transfer it to a vacuum desiccator
charged with sodium hydroxide pellets and leave it there for 2 days.
Extract the residue with hot chloroform and filter ; on cooling, crystals
of dimethylamine hydrochloride separate. A further crop can be obtained
by evaporating the filtrate to about half its original volume. The yield
is 120 g.



[Edited on 2-1-2009 by benzylchloride1]

octave - 2-1-2009 at 16:11

Could dimethylamine hydrochloride be produced from Hexamine and HCL with excess formaldehyde in solution as according to a section http://designer-drugs.com/pte/12.162.180.114/dcd/chemistry/m... ?

Jor - 2-1-2009 at 16:31

I recall formaldehyde and HCl should never be in contact with eachother, because Bis(chloromethyl) ether can form, wich is extremely toxic and a proven carcinogen.

octave - 2-1-2009 at 17:22

Well if the first reaction was completed which forms the methylamine HCL then the extra formaldehyde needed for dimethylamine hydrochloride would never come into contact with hydrochloric acid needed to form this Bis(chloromethyl) ether correct?

chemrox - 26-12-2013 at 16:07

Quote: Originally posted by garage chemist  
Dimethylamine can be prepared easily by boiling dimethylformamide with aqueous NaOH. Dimethylamine escapes as a gas and can be dissolved in water.
Buying dimethylamine is unnecessarily expensive and suspicious, as the substance is subject to chemical weapon control legislation, similar to e.g. PCl3.
Dimethylamine-borane is way too valuable to make dimethylamine out of it, get DMF instead.


~ 6M NaOH ??