Method 1: Synthesis of Guaiacol Himedia from methanol and catechol over Al-P-Ti-Si-O catalyst
In an aqueous solution containing a certain amount of aluminum source and vigorously stirring, drop the silicon source and the titanium source. After refluxing the phosphoric acid, reflux for several hours, heat in a water bath and evaporate to dryness. The obtained solid is ground into powder and dried at 393K for 12 h. , calcined in air at 673K for 5 h, pressed into tablets and sieved to obtain 40~60 mesh catalyst. The XRD analysis of the catalysts was carried out on a DM ax-rA type rotating target X-ray diffractometer, CuKα target, 40 kV x 150 mA. The specific surface area and pore structure test were carried out on a Micrometritics A SA P2010 specific surface area tester, and N2 was the adsorbate, which was adsorbed at the temperature of liquid nitrogen. The activity evaluation was carried out on a fixed-bed continuous flow reaction device: the reaction tube was a rigid glass tube (Ø1.1 am), and the amount of catalyst was 14 g (40-60 mesh). First pass into N before the reaction: purging reaction system, cut off Nz After adjusting to the required temperature, the reactant enters from the upper end of the reaction tube, and the product is condensed at the bottom of the reaction tube and flows into the collection bottle, n (catechol)/n ( Methanol) = 1/5, the feed rate is 0.5 mL/h, and the reaction temperature is 553K.
Method 2: Preparation of Guaiacol Himedia by o-anisole method
Include two steps: namely the diazotization of o-anisole and the hydrolysis of the diazonium salt, the former is a more common typical reaction in the diazotization reaction, as long as the appropriate acidity is controlled to avoid contact with harmful substances, and the control reaction is Performing at low temperature is basically quantitative; the latter is more complicated and is also the key to this method.
During hydrolysis, the diazonium salt loses the diazonium ion to generate phenyl carbocation. The slow reaction in this step is the control step of the hydrolysis reaction. The generated phenyl carbocation and the nucleophile water molecule are rapidly combined under the catalysis of copper ions. , a nucleophilic substitution reaction occurs to generate guaiacol, which is the main reaction, and the equation is as follows:
Method three: using catechol as raw material, and methylating reagents such as methanol and dimethyl carbonate under the action of catalyst to prepare guaiacol.
The catechol method is still in its infancy, and it is mainly studied in the laboratory, and there is no industrial report. The reaction mechanism is that catechol reacts with the methylating reagent first to form guaiacol, which is the main reaction; the generated guaiacol can further react with the methylating reagent to form phthalic ether, which is the main side reaction. . The general formula of the main and side reactions is as follows (in the formula CH3-X is a methylating reagent):