Hydroxyl boric acid complexation

Boric acid can form complexes with hydroxyl compounds. The control of the delay time requires control of the pH, the availability of borate ions, or both. Control of pH can be effective in freshwater systems [17]. However,... 

Figure 17-14. Formation of complexes of boric acid with glycerol. Three hydroxyl units form an ester and one unit forms a complex bond. Here a proton will be released that lowers the pH. The scheme is valid also for polyhydroxy compounds. In this case, two polymer chains are connected via such a link.

It was found in the first place that aliphatic, non-cyclic glycols without adjacent hydroxyl groups have no effect they cannot form cyclic complexes. But also most glycols with not more than two adjacent hydroxyl groups are inactive. I therefore assumed that only if two hydroxyl groups are favorably situated for the formation of a complex boric acid compound, will it be possible to observe an increase in the conductivity. 

Boric acid has the particular ability to form stable complexes with compounds that present cis-hydroxyl groups (cis-diol groups) [117]. Several compounds, such as sugars and their derivatives and some phenolics (o-diphenols) have these cis-diol groups and therefore can form stable complexes with B [117]. 

Boron is devoid of metallic character in water, it generates weakly acidic boric acid [B(OH)3]. This hydroxide bonds covalently with vicinal (neighboring) hydroxyl groups to form negatively charged, acidic complexes. 

In the D-fructosides the convention is that the more dextro-rotatory anomer is the a form. Attempts have been made by Boeseken and Couvert,82 Verschuur83 and MacPherson and Percival84 to apply Boese-ken s boric acid method to determine the configuration of D-fructose at C2. The problem is much more complex than for aldoses because there are three hydroxyl groups near the reducing center, and also because the mutarotation of D-fructose involves the conversion of some pyranose to furanose form with the loss of a pair of cis hydroxyls (on C4-C5). This work has been discussed by Boeseken88 but no conclusion has been reached. 

The constitution of the fairly strong complex acids formed from alkyl borates and alcohol and of esters of boric acid with polyalcohols with hydroxyl groups in the cis position (Boese-ken) must be similar ... 

In confirmation of this structure, Klimek and Parnas found that muscle adenylic acid forms a complex with boric acid. Such a complex has been shown by Boeseken to be formed only by polyhydroxy compounds having two adjacent ds hydroxyl groups. 

Chemically reactive systems are those in which a special effect, in addition to partition and/or adsorption, lends added selectivity to the system. Examples include use of chemically modified cellulose (carboxyl paper), ion-exchange papers [34], or papers impregnated with a selective reagent (e.g., boric acid [35] for separation of various hydroxyl compounds), or the mobile phase may contain a reactive or complexing reagent in combination with normal or modified cellulose [21]. 

Boric acid forms ester complexes with hydroxyl groups of organic compounds preferably occurring when the hydroxyl groups are adjacent and cis (Hunt 1998). The importance of the proper hydroxyl arrangement is demonstrated by the fact that poly-... 

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