1. Synthesis of p-bromobenzaldehyde with p-nitrotoluene
p-Bromobenzaldehyde is an important pharmaceutical and dye intermediate. The existing method for synthesizing p-bromobenzaldehyde mainly uses p-bromotoluene as a raw material. One is to generate benzyl dibromobenzene through a photochemical bromination reaction, which is then obtained by hydrolysis. The method has been industrialized. Cerium methyl sulfate is obtained by oxidation of oxidant. Their common disadvantage is that the cost of raw materials is high, and the former uses highly volatile and hazardous liquid bromine, while the latter adopts an oxidation method that is difficult to control industrially.
CN97106992.1 proposes a method for synthesizing p-bromobenzaldehyde with p-nitrotoluene as raw material. In the present invention, p-nitrotoluene is used as a raw material, and under the catalysis of a phase transfer catalyst, a disproportionation reaction occurs with a sodium polysulfide solution to generate p-aminobenzaldehyde. Under the catalysis of copper or copper, p-bromobenzaldehyde is generated. The sodium polysulfide solution is formed by the action of sodium sulfide (Na2S.9H2O) and elemental sulfur. The molar ratio of sodium sulfide to sulfur is 1:2-1:4. Sodium polysulfide and p-nitrotoluene are in 95%-65% ethanol solution under the action of phase transfer catalyst to produce p-aminobenzaldehyde, and a small amount of p-toluidine is produced. The molar ratio of sodium polysulfide to p-nitrotoluene is 1:3-1:5, the addition amount of the phase transfer catalyst is 1%-5% of the amount of p-nitrotoluene participating in the reaction, and 1 mol of p-nitrotoluene is required to participate in the reaction. 95% ethanol 400-600ml, the reaction temperature is 80-90℃. Under the above conditions, the yield of p-aminobenzaldehyde is >90%.
The phase-transfer catalyst adopted is one of tetrabutylammonium bromide, cetyltrimethylammonium bromide, tetrabutylammonium iodide, N-dimethylformamide, Tween or a mixture of two thereof. Mixed phase transfer catalysts work better. The obtained p-aminobenzaldehyde is distilled by steam, and crystallized by cooling to obtain the wet product, which directly participates in the next step reaction without drying. The acidification of p-aminobenzaldehyde uses sulfuric acid as acidifying agent and sodium nitrite as diazotizing agent. After the diazotization is completed, drop the diazonium salt solution into the newly prepared cuprous bromide hydrobromic acid solution or the newly prepared reduced copper hydrobromic acid suspension. After 1 hour, steam distillation was carried out, and the distillate was filtered and washed to obtain colorless or pale yellow p-bromobenzaldehyde. Purity >98%. 1mol of p-aminobenzaldehyde needs 0.5-1mol of cuprous bromide or 0.05-0.1mol of reduced copper to participate in the reaction, and 2-3mol of hydrobromic acid is required. The preparation of cuprous bromide adopts the usual method. The yield of p-bromobenzaldehyde relative to p-nitrotoluene was 55-65%. The invention provides a method for synthesizing p-bromobenzaldehyde by using p-nitrotoluene as a raw material. By adopting the method to synthesize p-bromobenzaldehyde, the cost of raw materials is low, the industrialization is easy to be realized, and the product purity reaches 99%.
2. For the synthesis of DSD acid
4,4′-Diaminostilbene-2,2’disulfonic acid (DSD acid for short) is an amphoteric compound that contains not only an acidic group sulfonic acid group, but also a basic amino group, which can directly It has condensation reaction with cyanuric chloride, and can also be coupled with most aromatic compounds after diazotization. Therefore, using DSD as raw material, a series of direct dyes, acid dyes and reactive dyes can be synthesized.
At present, the process route for synthesizing DSD acid in most domestic manufacturers is that p-nitrotoluene is sulfonated to generate p-nitrotoluene-o-sulfonic acid (NTS acid for short), and then oxidized in an alkaline medium to generate 4,4′-dinitro stilbene-2,2′-disulfonic acid (referred to as dinitro acid or DNS acid), and finally obtained DSD acid by reduction. CN201510732494.7 provides a DSD acid synthesis process, which combines electrodialysis and bipolar membrane electrodialysis to replace the salting-out step in the traditional process. The usage of the raw material salt reduces the salt content in the subsequent reaction, and at the same time makes full use of the inorganic resources generated in the process, improves the quality and yield of the product, and reduces the process cost.
A DSD acid synthesis process is characterized by comprising the following steps: (1) p-nitrotoluene is subjected to a sulfonation reaction to generate p-nitrotoluene-o-sulfonic acid; (2) p-nitrotoluene-o-sulfonic acid is subjected to The oxidative condensation reaction obtains an oxidative condensation reaction solution; the oxidative condensation reaction solution is treated by electrodialysis to obtain an organic solution containing an intermediate product 4,4′-dinitrostilbene-2,2′-disulfonic acid (DNS acid) and containing brine; (3) subjecting the organic liquid in step (2) to reduction reaction and acid precipitation to obtain a DSD acid product; the brine containing brine is treated in a bipolar membrane electrodialysis system to prepare aqueous sulfuric acid, aqueous sodium hydroxide and dilute brine ; Sulfuric acid aqueous solution and sodium hydroxide aqueous solution can be reused in the DSD acid synthesis process respectively.
3. Synthesis of p-hydroxybenzaldehyde from p-nitrotoluene
With the increasing use of p-hydroxybenzaldehyde, the domestic and foreign market demand is also increasing. Domestic and foreign manufacturers and research departments have been conducting long-term and in-depth research on its production process, and there have been a large number of research reports. . At present, there are mainly 6 kinds of production processes reported at home and abroad, two of which are the most worthy of attention: one is a two-step classical synthesis process using p-nitrotoluene as raw material, redox first, and then diazotization reaction. , the synthesis reaction scheme is shown in Figure 1; the other is a new synthesis process that uses p-cresol as a raw material, under the action of a mixed catalyst of cobalt and copper compounds, and synthesizes the target product through pure oxygen oxidation.
