Sciencemadness Discussion Board


reidy2015 - 20-3-2015 at 20:28

Question about paraformaldehyde. What would happen if I refluxed paraformaldehyde with ethanol or methanol temperature unknown or reflux time unknown . To change it back into formaldehyde. Can it be done yes or no :)

[Edited on 15-03-2015 by reidy2015]

Chemosynthesis - 20-3-2015 at 21:06

You don't know reflux temperatures?

reidy2015 - 20-3-2015 at 23:04

No I don't know what temp and how much paraformaldehyde and ethanol to use. But put it this way I do under basic chemistry but still learning.

Chemosynthesis - 20-3-2015 at 23:13

You should probably post this in Beginnings next time. Reflux temperature occurs at the boiling point of your solvent. This is usually covered very early on in chemistry or physics in thermodynamiucs, but you might not be there yet. It is pretty basic, so you should learn it. What sources are you looking at? Have you done any research at all?

I usually adjust the pH, but you can find an answer in the literature; example Biotech Histochem. 2000 Jan;75(1):19-22. What are you using this for, if anything? That and saturation will determine how much of what you use, for concentration.

reidy2015 - 21-3-2015 at 00:19

Sorry I'll post from the beginning next time. True on what you say boiling points of chemical formulas.I've done a little research on this limited information I have.Interesting you adjust the ph. I'll look that up have a read. Purpose I'm interested in doing this is learning since I have some paraformaldehyde and ethanol or methanol to do a experiment. Thanks

Haber - 21-3-2015 at 04:42

Refluxing paraformaldehyde in methanol for 40-60 minutes is a convenient method for preparing a methanolic formaldehyde solution.

I've made 40% solution this way, works like a charm.

[Edited on 21-3-2015 by Haber]

[Edited on 21-3-2015 by Haber]

reidy2015 - 21-3-2015 at 17:49

Thanks haber :cool:.

reidy2015 - 21-3-2015 at 18:46

Found some information what I'll is heat 50 ml of hot distilled water to the water I'll add one drop 37% sulfuric acid followed with 37 grams of paraformaldehyde adding the paraformaldehyde in small amounts till it all put in with magnetic stirring. Then adding another drop of sulfuric acid if paraformaldehyde is not dissolved probably. Followed 100 mill of distilled water on what ever percent of formaldehyde you want. A question to ask if I want to make the formaldehyde stable. Can I add 10 or 15% methanol to made it stable. For storage

reidy2015 - 21-3-2015 at 18:57

After I do this experiment what could I put with the formaldehyde like a acid to do alkliod testing and information on how I could to this . To identify a alkliod is present in natural plants leaves bark etc .

Chemosynthesis - 21-3-2015 at 19:08

Where did you get the numbers from? You should look into the solubility of formaldehyde in your solvent... because 37g paraformaldehyde in 50ml of water might be asking for a nasty surprise.... Go see how much formaldehyde can dissolve in water. Then see what phase formaldehyde is in. What will happen when you exceed the saturation point in water? Now check to see what the conversion of paraformaldehyde to formaldehyde is.

Stabilization. It may not even be necessary, depending on how long you wish to store it, but yes, generally this is acceptable, and often how it ships from supplier. From my previous citation:

Biotech Histochem. 2000 Jan;75(1):19-22.
Formaldehyde prepared from paraformaldehyde is stable.
Helander KG1.

"For critical histological investigations, tissue fixation is sometimes carried out in formaldehyde freshly prepared from paraformaldehyde by heating. The purity of formaldehyde produced in this way is superior to that of commercial stock solutions. We studied the stability of freshly prepared formaldehyde solutions by determination of pH and titration of acid, which reflect the formation of formic acid. It was found that very small amounts of acid are produced during the heating of paraformaldehyde. Prolonged heating or storage of freshly prepared formaldehyde for up to 8 days did not significantly increase the amount of acid. It was also found that heating of the paraformaldehyde is not necessary, since depolymerization may take place at room temperature. We conclude that formaldehyde prepared from paraformaldehyde remains stable for considerable periods of time, and it is therefore unnecessary to prepare it immediately prior to fixation. Also, in many cases, buffering of the fixative may be omitted, since only minor changes in the pH occur during fixation."

reidy2015 - 21-3-2015 at 20:12

Yes found my answer with your answer thanks. Makes sense now. So paraformaldehyde in distilled water with stirring adding right amount of water till paraformaldehyde is dissolved completely =fresh formaldehyde then for storage add 10 percent methanol to stop it oxidising. Then preparing formaldehyde or formalin at 37% or 40% by mixing 1:10 with a phosphate buffer with it in step one ;)

morganbw - 22-3-2015 at 08:56

Quote: Originally posted by Chemosynthesis  
You don't know reflux temperatures?

I have found that dissolved items do not always re flux at the solvents boiling temp. Perhaps my thermometer is no good?

Molecular Manipulations - 22-3-2015 at 11:40

Perhaps. Or an azeotrope forming is another possibility. It depends on the nature of the solute (and solvent). Sugar changes the boiling point of water, allowing saturated solutions of sugar water to boil at over 150 degrees C, depending on the concentration.
Ammonium chloride makes water freeze at -17.777 degrees C or 0 degrees F (this mixture is how the Fahrenheit scale was first calibrated).
Point is, impurities can easily change the boiling/melting temperature of substances.

reidy2015 - 22-3-2015 at 16:34

I'll do some tests on this found out if you got just under a gram of paraformaldehyde in 2.5 grams of h2o then make a mixture of 35 mil of 1n koh magnetic stirring and heating to a low 50 to 60deg then filter then store the formaldehyde at 4 c. After doing some research wow chemosynthesis opened up pages of information on this ill be reading for the next two months studying. Lol