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Topic: Glycol borate ester precipitation  (Read 4711 times)

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Offline Savian

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Glycol borate ester precipitation
« on: April 29, 2010, 12:25:26 AM »
I'm sorry if this is the wrong forum.

I have a roughly 1.7:1 molar ratio of ethylene glycol to boric acid (in a little water), which is known to form glycol borate esters.  The degree of ligand substitution (1:1 to 2:1) is determined by the pH:  the higher the ph and the higher the glycol molar ratio, the greater the substitution.  The base in this case is sodium hydroxide.

I found a paper that indicated that the level of glycol borate ester formation became saturated at pH = 11.  Considering that there is enough caustic in the formulation to bring the ph to >13 (and probably well beyond):

(1) it's probably safe to say that, on average, there are 1.7 mols of ethylene glycol bound to every mol of borate [B(OH4)] in this solution.

(2) are there any obvious answers - particularly concerning solubility - to explain why, after about a week, such a blend would crash out a white precipitate, which by FTIR analysis has indicated the presence of a crystallized borate complex that is not boric acid?

(3) could the same sort of complex be the cause of the formation of a brick red particulate at the surface of the liquid (presumably because of an interaction with oxygen) over a period of several days/weeks?

(4) is there any known relation between solutions of boric acid/sodium hydroxide and stainless steel?  The problems I've mentioned only seem to occur when the product has been stored in stainless steel - it doesn't happen in plastic bottles.

Believe me when I tell you that I've done my homework on this.  I'm just desperate for answers and I'm running short on time.  Thanks in advance for the replies.

>S

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