| 摘要 |
<p>The two-stage oxidn. is effected under acid conditions. Stage (a) is an oxidn. - addn. reaction effected in homogeneous phase at 70-115, pref. (80-110) degrees C. A soln. of 2:6-dimethylpyridine in 50-80 (60-70)% H2SO4 contg. 2:6-dimethylpyridine in such amt. that after the oxidn. reaction, the amt. of free acid is 30-20 mol.; pref. 6-10 mol/mol. dipicolinic acid formed, is reacted with a 40-65 % pref. 45-50% soln. of a sol. salt of hexavalent Cr (calc. as CrO3) in 10-100 (20-50)% excess over the stoichiometrically equiv. amt. Both organic and inorganic reactants are admixed slowly over 2-3 hrs., and the reaction is then effected for 0.5-3 hrs., pref. 1-2 hrs., depending on the temp. With elimination of 1 mol. water, there is obtd. as intermediate, an adduct of dipicolinic acid and chromium oxide. The reaction mixt. is cooled and the adduct centrifuged and washed. In stage (b), the above intermediate is hydrolysed at 50-100 degrees C, pref. 80-100 degrees C, with 5-15, pref. 9-11 times of water w.r.t. the total wt. of solid material (calc. as dry substance, the amt. of CrO3 in the hydrolysis liq. being is not >6-7%, pref. 4%. The hydrolysis time is 0.5-4 hrs., pref. 1-2 hrs. and the pptd. dipicolinic acid is centrifuged, dried and recrystallised from water. The dipicolinic acid is obtd. in purity of 9.5 plus-or-minus 0.2%. It finds use in the synthesis of polyester and polyamide copolymers; as stabilisers for peroxides and per-acids; as polishing soln. components for metal surfaces; as stabilisers for epoxides, organic substances and photographic emulsions or solns. where it inhibits the pptn. of Ca salts.</p> |
