Calculate the hydroxyl value (hydroxyl number) of organic compounds using sample weight, titration volumes, and acid normality for accurate chemical analysis.
Hydroxyl Value
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Hydroxyl Content
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Equivalent Weight per OH
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Hydroxyl value is the number of milligrams of potassium hydroxide equivalent to the hydroxyl groups in one gram of sample. It's crucial for characterizing polyols, determining molecular weight, and quality control in polymer and resin manufacturing.
Samples should be dried and free from moisture. Weigh accurately (typically 1-5g) and ensure the sample is completely dissolved in the acetylation reagent. The sample should contain sufficient hydroxyl groups for accurate titration.
Method A uses acetic anhydride in pyridine for acetylation, suitable for most samples. Method B uses phthalic anhydride in pyridine, preferred for samples containing amino groups or other interfering compounds that react with acetic anhydride.
Common causes include incomplete acetylation, moisture in samples or reagents, incorrect normality of titrants, incomplete dissolution of sample, or presence of interfering compounds. Ensure proper drying and use fresh reagents.
Hydroxyl values vary widely depending on the compound. Low molecular weight polyols may have values of 500-1500 mg KOH/g, while high molecular weight polymers typically have values below 100 mg KOH/g.
Temperature affects both the acetylation reaction rate and completeness. Most methods specify reaction temperatures of 95-100°C for 1-2 hours. Higher temperatures may cause decomposition, while lower temperatures may result in incomplete reaction.
This calculator works for most hydroxyl-containing organic compounds including polyols, alcohols, and hydroxyl-terminated polymers. However, compounds with sterically hindered hydroxyl groups may require modified conditions or different analytical methods.