Sciencemadness Discussion Board

improvised device for aromatic aldehydes.

BasementBill - 15-3-2008 at 13:00

I'm researching how to reduce an aromatic carboxcylic acid into it's corresponding aldehyde, specifically Salicylic Acid in Salicylaldehyde. I've attached a nifty article that promises a 92% yield using Titatanium(IV)Oxide and formic acid. However i cannot grasp what their apparatus is. or why they are using it. so my questions are;

i) what the heck is it?
ii) would a steal pipe in an oil bath do the same thing?
iii)is this thing at high risk to explode? :S

also if your interested in this you might also enjoy, http://www.designer-drugs.com/pte/12.162.180.114/dcd/pdf/aro...
(NOT THE RELEVENT ARTICLE)



"Apparatus.--A mild-steel tube A, 2 ft. 4 in. long and of 1& in. internal and 2 in. external diameter, is fixed
concentrically inside a mild-steel tube B, 2 ft., and of 23 in. internal and 3 in. external diameter, by means of female
joints which are each connected to the ends of A and B by 12 screw threads, into which in turn screw 2 plugs C. The
annular space between tubes A and B is filled with a low-melting fusible alloy, and tube B contains a circular aperture
of 4 in. diameter to which is cemented a short ring, .l in. deep and of in. internal and 1 in. external diameter, which is
filled with the alloy of the annular space; this outlet serves as a thermometer pocket, and as an overflow outlet when
expansion occurs. The apparatus is arranged lengthwise on a wooden stand, and tilted at an angle of ca. 20" ; it is heated
from below by two batswing Bunsen burners.

Method of Working.-
The sealed Carius glass tube, charged with the reactants, was inserted in the inner tube A by means of a short wooden stick, and the plugs C screwed into position. Heat was then applied, and alloy abstracted or added via the outlet as occasion required, and when the reaction was completed, the apparatus was allowed to cool, plugs C were removed, the glass Carius tube was pushed so that one end just protruded from the upper end of A, the lower end being first packed with cotton waste or similar material, and then secured again to absorb the shock due to recoil after the tube had been opened in the usual manner. The following example is typical of the general procedure employed, and the results for 11 carboxylic acids are included in the table below.

Preparation of Lauric Aldehyde.
-Lauric acid (0.1 g.-mol,), 95% formic acid (0.1 1 g.-mol.), and titanium dioxide
(0.5 g.) were charged into a Carius tube of ca. 15 in. in length and 1 in. internal diameter, which was inserted in the above
apparatus, heated to 260" during 3 hours, and maintained at 250-260" for 2 hours. After cooling (generally by keeping
overnight) to room temperature, the residual pressure was released, and the contents of the tube removed by ether
extraction (ca. 50 c.c.). The ethereal extract was filtered from titanium dioxide, washed with x-sodium hydroxide to
remove unchanged carboxylic acid, then with water, dried (calcium chloride), filtered, and the ether removed : the
residue (6-5 g.) was a colourless oil. Estimation of the aldehyde content by the hydroxylamine method (Stillmann and
Reed, Perfume and Essential Oil Becord, 1932, 279) indicated 5.7 g. of lauric aldehyde. The crude oil above was purified
via its bisulphite compound in the usual manner, and. then had m. p. 38-39.5', b. p. 238", da!" 0-9213. The alkaline
filtrate above, when acidified and extracted with ether, afforded 13.1 g. of unchanged lauric acid. The conversion was
therefore 31%, Le., a yield of 90% on the lauric acid consumed."

thanks for your insights.

Attachment: JR9430000084.pdf (302kB)
This file has been downloaded 661 times

not_important - 15-3-2008 at 19:29

Quote:
Originally posted by BasementBill
I...my questions are;

i) what the heck is it?
ii) would a steal pipe in an oil bath do the same thing?
iii)is this thing at high risk to explode? :S

...


i) just what they said. Two tubes arranged concentrically, somewhat like a metal Liebig condenser, the space between them filled with a low melting alloy. It has plugs that can inserted to block the tubes off. The liquid alloy serves to transfer heat from the burners to the inner tube and its contents, evening out hot spots and preventing too quick of heating.

ii) Why steal pipe, most hardware stores will sell you lengths of pipe made of a number of different material, for not that large of a sum.

An oil bath with a single tube immersed in it would work, if the oil is usable at 260 C. At the time this was written liquid metal baths were the best option for that temperature. The concentric tubes reduce the amount of allow needed as compared to a normal 'pot' bath.

iii) it might, sealed glass tubes do in a small percentage of cases, especially among the inexperienced who tend to bollix up the seal so it's too weak.

microcosmicus - 15-3-2008 at 20:41

Quote:

is this thing at high risk to explode? :S


That is why the thing is enclosed in a steel pipe --- should the glass tube
rupture, a quarter-inch of steel will contain the explosion. The remaining
risk is that of the organic mix which was in the tube starting a fire so you should
take suitable fire precautions like not doing this near anything flammable.
Also, when doing this nowadays, use electric heating rather than open
flames (e.g. wrap resistance wire around the outer tube) to further reduce
fire hazard should anything go wrong. If you are using oil than metal,
make sure the flash point of the oil is above 260C. Probably that will
mean using a silicone oil, but you need to pick one made for high temperature
because not all silicone oils are up to the task. For more information, see
Hart Scientific's guide to temperature baths:

http://www.hartscientific.com/products/bathfluid.htm

Since silicone oil tends to be pricey, other alternatives are worth
considering,. One possibility is asphalt. According to the book
"Roofing Failures" by Carl G. Cash (p. 22 in the introduction):
Quote:

Most roofing asphalts have a flashpoint in excess of 260C. This
is only slightly higher than the carbon-hydrogen excitation temperature
of about 250C where the asphalt starts to degrade (where the
vibrating carbon and hydrogen atoms tend to fly apart) and
quite close to the average temperatures encountered in the kettle
where the asphalt is melted.


So the bad news is that pretty much the same reason you want to heat
the organics inside the tube are going to ruin the organics outside the
tube but the good news is that roof tar is cheap enough that you can
use some once and throw it away and use fresh asphalt the next time.

Since the purpose is to act as a heat bath and transfer heat, a solid
would do just as well. For instance, magnesia or the good old sand bath.

[Edited on 16-3-2008 by microcosmicus]