Currently, organic synthesis has become one of the most important subjects in the field of chemistry and played an important role in research, industry and business. It is well known that synthesis reaction is the interaction of two different atoms or molecules to form other molecules or compounds. Then, does the quality of the reaction materials affect organic synthesis?
The answer is YES, very important. In the process of synthesis process research, starting materials are the basis of synthesis research work, directly related to the quality of the end product and process stability, and even involve labor protection and safety production issues in industrial production. Therefore, at the beginning of the synthesis reaction, there must be quality requirements for the starting materials.
For example, the quality standards of the starting materials, the supplier’s inspection reports, the standards of impurities or isomers introduced by the starting materials, etc., if necessary, internal control standards can be established according to the requirements of the preparation process.
This article will continue to talk about organic synthesis from the following aspects.
1.What is organic synthesis?
Organic synthesis is the process of preparing simple inorganic substances or simple organic substances into more complex organic substances by chemical methods. Therefore, in more cases, organic synthesis is much more complicated than general A+B→C. In other words, organic synthesis is that uses basic and readily available raw materials and reagents, coupled with human wisdom and technology to create more complex and peculiar compounds.
2. 7 factors that affect the quality of reaction material
Generally speaking, we need to check the reaction material quality before starting. I will describe as following 7 tips:
2.1 The purity
Chemical purity plays an important role in the organic compound reaction. It has commonly been assumed that low purity will lead the reaction incompletely. On the other side, raw materials with low purity will bring more impurities which will participate in new reactions and cause a lot of trouble for the finished product.
2.2 Moisture
For some special synthesis reactions, such as Grignard reaction, Friedel-Crafts reaction, Condensation reaction, etc., there will be special requirements on the quality of raw materials. For reactions that must be carried out under dry conditions, strict requirements, and control of the moisture content in the starting materials are required. If the moisture content of the raw materials is high, it may directly cause these reactions not to occur, and even prone to explosion for some hydrogen catalytic reactions.
2.3 Loss on drying
This index is required for most raw materials. If the loss on drying content is higher than the standard, it may lead to insufficient raw material feeding in the reaction, resulting in incomplete reaction, thereby affecting the purity and refining process of the final product.
2.4 Trace elements
Usually, the trace elements contained in the raw materials are difficult to remove, and they are usually left to the final product along with the reaction, which has a great impact on the quality of the final product.
For example, in the preparation process of raw materials, the control of trace elements is an important and effective measure to ensure drug safety.
2.5 Content of impurities or isomers
If the impurities in the raw materials cannot be removed during the reaction process or the impurities participate in the reaction, it will definitely affect the quality of the final product.
Therefore, the raw materials that have a certain impact on the product quality must have corresponding standards. And need to note the impact of changes in raw material specifications during process optimization on product quality.
It is also necessary to pay attention to a certain limit on the content of the isomers, so as not to affect the quality of the finished product.
2.6 Existence of starting materials
Some synthesis reactions will also affect the yield due to the existence of the reaction raw materials.
For example, in the synthesis of ethyl acetoacetate, the state of the reaction raw material sodium (sodium beads, sodium wire, sodium block) determines the reaction time and yield. Many scholars hold the view that the effect of sodium beads is the best and the effect of sodium blocks is the worst.
Another example, diallyl phenol has two appearance states, one is a colorless transparent liquid and the other is a light yellow transparent liquid. It has been reported that the color of the raw material easily affects the color of the final product during synthesis.
2.7 The manufacturing date of raw material
It is a widely held view that the raw material needs to be tested again to ensure the compound process smoothly if out of the expiration date. Otherwise, it will bring trouble to the synthesis work.
3. Other factors affecting the result of the synthesis reaction
3.1 Feeding ratio in reaction
In theory, most synthetic reactions are carried out according to a certain ratio, but the reaction feed ratio does not match the theoretical value in actual production.
For example, in the synthesis experiment of acetanilide, the theoretical raw material aniline and glacial acetic acid feed ratio are 1:1, but 1.1:2.6 in practice. This is because the reaction is reversible reaction. Appropriately increasing the amount of raw materials can promote the reaction to move in a positive direction and increase the yield.
Another example is the intramolecular ester formation reaction of (2-hydroxycyclohexyl) acetic acid. Intramolecular reactions can occur to form lactones, and intermolecular reactions can also occur to form esters. At this time, the concentration of raw materials must be controlled to reduce intermolecular side reactions.
Therefore, in the synthesis process, the amount of raw materials with lower prices and convenient supply can be appropriately increased. Generally, an increase in 5%-20% and individuals can increase by more than 2-3 times.
3.2 Feeding sequence and feeding method
For some chemical reactions with greater thermal effect, the feeding order has a great relationship with the yield of the final product. It is almost certain that there is big difference in yield due to the different feeding order for same raw material. The wrong feeding method will make the concentration of the materials in the system uneven which will cause various side reactions.
For example, during methylation of phenol by dimethyl sulfate, if the dimethyl sulfate is fed too fast and cannot disperse quickly, will result in a high local concentration and lead to hydrolysis side reactions. The same is true for hydrazine hydrate and hydrogen peroxide.
In addition, easily decomposable raw materials need to be added in batches or dropwise to avoid local over-concentration leading to decomposition side reactions.
3.3 Reaction temperature
During the reaction process, improper temperature control often leads to the occurrence of side reactions and the loss of some raw materials. In addition, depending on the reaction temperature, the proportion of the final product will also vary.
For example, in the process of preparing naphthalenesulfonic acid using naphthalene as a raw material, when the reaction temperature is controlled below 60 degrees, the output of a-naphthalenesulfonic acid accounts for 96%, while the output of B-naphthalenesulfonic acid only accounts for 4%. When the reaction temperature increased to 165 degrees, the output of a-naphthalenesulfonic acid dropped to 15%, but the output of B-naphthalenesulfonic acid rose to 85%.
Therefore, after the product is determined, the yield changes in different temperature ranges must be fully considered, and the appropriate reaction temperature must be selected to obtain the best yield.
In addition, a large number of experimental studies have shown that the control of the hydrogenation reaction temperature is particularly important.
3.4 pH
In some synthesis reactions, the pH of the reaction has an important impact on the yield of the final product, especially the hydrolysis, esterification and other processes, which are more affected by the degree of acid-base.
For example, when silicon nanomaterials are prepared by the hydrothermal method, the pH of the solution is an important factor in the formation of silicon nanomaterials.
3.5 Reaction time
In most synthesis reactions, if the reaction time is not enough, it will lead to an incomplete reaction of the raw materials and affect the yield of the final product.
For example, if the reaction temperature is 200℃, the molar ratio of phenol to dimethyl carbonate is 1:2, the amount of catalyst is 3%, and the KCl loading is 15%, the phenol conversion rate can reach 100% when the reaction time is 10h.
4. Conclusion
The above summary is some insights from many years of industry experience. In actual production work, it is necessary to study each link of production one by one according to the total yield and quality of the product.
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