Melting point significence

[SHORTY]

If one were to test the mp of meth made using pseudo/i2/hypo and found the mp to be 162C then what might he possible have. In other words is it common for the mp to be off by 10 degrees when working in a clandestine lab?

I should also add that the mp test was done ghetto style by using a oven.  I put the meth in a glass dish and covered it with glass lid and setup a thermometer right next to it and slowly increased the temp over about 30 minutes.  At 162C the crystals melted into a small puddle without any visible smoke.  Should the substance vaporize at its melting point or just become a liquid?

[ADDkid]

While melting points are helpful, I would not get down if the melting point is too off, because just a small percent of impurities can manipulate it drastically.  Melting are good tools, but I am starting to believe that the best tools, are tools like Jones reagent, Tollens test, Lucus test and so on, in the combination of other neat and efficient methods describe in Vogels 5th Ed.  Also, sitting down and figuring out all the side products, (except for bullshit denaturants found it p-fed) and using that information to correctly separate, based on the properties, this method is also found in Vogels 5th Ed.  One more thing, the polarimetry tools is cheap I think, and might be also very helpful.  One could probably just make one.

P.S.  Swig suggest that you find the kind of test that you will need in order to identify any compound that you are likely to run into or synthesize, and before doing anymore reactions make little bottles labeled with there names, (one might use iodine tinc. Bottles) however, Jones reagent seems to eat the top off. Then buy little droplets tubes and then you can run many tests very fast and mess is limited.  Here is a site for most common test, although many more can be found.  These tests are very fun because of the visual and smell changes.  Tollens test produces a mirror with aldehydes.  When swig made benzyl bromide with benzyl alcohol and HBr, Jones test was used to see if the reaction was completed, then swig notice the smell of benzaldehyde very strong, which lets me know that primary alcohol was still present, and the most important, Benzaldehyde has the possibility of being produced and isolated in great yields using the Jones reagent.

http://www.chemistry.ccsu.edu/glagovich/teaching/472/qualanal/tests/tests.html

P.P.S.  When doing the Melting point test in the lab, it seems to turn in to a liquid first and then vaporizes (depends on the compound),  It happens very fast, before it happends it has very faint melting appearants, and then once the point is acheived it has a crumble like visual affect right before it melts, but that is only when using mel-temp.

[CharlieBigpotato]

[ADDkid]

[CharlieBigpotato]

[ADDkid]

[WizardX]

Tech Grade Solvents can also affect the substrate melting point, because the solvents have impurities. Use a LR grade solvent (or even better AR) with recrystallisation to improve the purity.

[kris_1108]

[Osmium]

> I should also add that the mp test was done ghetto style by using
> a oven.  I put the meth in a glass dish and covered it with glass
> lid and setup a thermometer right next to it and slowly increased
> the temp over about 30 minutes.

This is extremely unreliable. Use an oil bath, a small glass test tube (the smaller the better) and a thermometer. Professional MP apparati use thin glass capillaries (about 1mm diameter) and a magnifying glass to observe the sample, and they only require a few milligrams of material for a MP determination.

[Newton]

Plus, check that thermometer! By sticking it into boiling water and see if the temperature shown is 100°C +- 1°C.

SWIM had exactly that experience with his first ever meth run. Thermometer showed 160°C at melting point   , but it later turned out that the actual temperature was 172°C !  This was confirmed with several (mercury) thermometers. The original one probably contained alcohol. What kind is the one you used?

[SHORTY]

The thermometer test has been done in boiling water and it is working fine.  It is the mercury type 0-200C.  However, my oven theromostat is about 30 degrees off.  No wonder it takes longer than it should to bake cookies!
I know that the proper way is in a oil bath but i don't understand why the way i did it would be so unreliable.  The temp was brought up at a very slow rate and the bulb of the thermometer was fitted right next to the sample being tested.  Also, i use only lab grade solvents. 

Next time i will put a little pseudo in at the same time to see if it is off as well.

[Newton]

I know that the proper way is in a oil bath but i don't understand why the way i did it would be so unreliable.

The breaking of the crytal lattice (melting, that is) requires energy. So heat is taken up, causing the melting sample to be colder than the environment. This effect will be smaller when oil is used (separated by a thin glass tube wall), as oil has a much larger thermal coefficient than air.

[SHORTY]

That the melting point would have been even lower if i had done the test in oil?

Also, by increasing the heat at a slow rate (1-2 degrees a minute) wouldn't this give a more accurate calculation?

Does the substance being tested have to actually vaporize or just become liquid when testing for the mp?

[MarleyBob]

The temp was brought up at a very slow rate and the bulb of the thermometer was fitted right next to the sample being tested.

Even in the school lab when I use the real mp testers, its not uncommon for the reading to be 5 or so degrees below what it really is. To get a completely accurate mp test a lot of patience is required, the temp has to be risen very slowly

The fact your reading is 10 degrees below sounds just about right to me for a clandestine setting.

[MarleyBob]

shorty: mp test requires the solid be turned to a liquid

liquid to vapor is bp test  

Slowness is key!

[SHORTY]

So what is the bp of meth?

[Newton]

That the melting point would have been even lower if i had done the test in oil?

Yeah, you're right. SWIM's original argument should be applied to the bulb of the thermometer, which probably has a larger thermal coefficient than the meth.HCl, and gets warmed too slowly by the air, while the sample has already melted.

All these considerations are under the assumption that the actual mp of your sample _is_ higher than 160°C. It maybe that it is impure, although this is not likely considering the cleaning step Shorty usually performs (this stuff was A/B-ed, steam distilled and recrystallised, right?).

So what is the bp of meth?

SWIM was wondering about this as well not long ago, Rhodium was kind enough to point out that meth-HCL does not have a bp. It starts to decompose before actually boiling.

[SHORTY]

What is the temp at which it has to be heated in order to smoke it?  Or what is the heat at which it decomposes?  Does it have to decompose in order to smoke it?

[Rhodium]

When you smoke meth, part of it will decompose (to more or less healthy degradation products, see the FAQ), and part of it will sublime/vaporize (forming an aerosol of intact meth.HCl). The higher the temperature and the longer the heating, the more degradation will occur.

[Phlegm]

I find this melting point stuff interesting. I have two apparati that measure melting points purchased as surplus for about $50 each. Fisher-Johns and Elctrothermal brands. They're both old, but were lab standards for years. In fact, I think the Fisher-Johns is still marketed virtually unchanged from the past. Anyway, I bought some commonly available compounds as calibration standards. Both instruments gave almost identical results to Merck's published melting points. So, my confidence in them is high.

Merck lists MA as having a melting point of 170-175 C., which is somewhat broad compared to most compounds. I  tested my last three batches and they came in at 172-174, 170-173, and 174-176. Now, of course, I believe that my shit is some of the best around. But I do not belive that is 100% pure. What I need to research is how much contamination can a compound typically contain and still spec out very close to it's true melting point/range.

As far as rigging a homemade apparatus, I spent a fair amount of time thinking about one and actually started making it, but abandoned it. I just don't think it's worth the time investment. With some searching you can find one reasonably priced.