(3) Principles for the design and selection of synthetic routes
The design and selection principles of the synthetic route include the following aspects
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1.
The principle of raw material selection
Cheap and easy to obtain; low risk, try to avoid the use of flammable, explosive and toxic materials; use environmentally friendly raw materials, avoid strong acids and strong alkalis and highly polluting materials, and choose green, environmentally friendly, atomic economy (high atomic utilization) reagents or raw materials
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2.
The process should be simple
There are few steps, simple route, avoiding too long and complicated; simple operation, avoiding complication; easy to separate, high yield; reaction and post-treatment are best at room temperature and pressure, avoid high temperature, high pressure, high vacuum or too low temperature, which is extremely demanding Will lead to a series of high investment and dangerous problems
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3.
Low cost, high yield and quality
Low cost, high yield and high quality are the ultimate goals, but the three must be built on the basis of safety, and the cost of accidents cannot be ignored
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4.
Safety must be implemented in the entire design principle
In short, the selection of raw materials, the determination of the process, the trade-off between yield and cost, and safety assessment are all related to the design and optimization of the synthesis route
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In the process of designing and optimizing the synthetic route, it is very important to always insist on putting safety in the first place.
You cannot wait for an accident to consider how to redesign a new route
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2.
Qualitative assessment of reaction risk
The qualitative assessment of the risk of a reaction refers to a comprehensive assessment of the chemical nature and chemical process of the reaction, the physical nature and the physical process, the equipment and the environment involved
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(1) The first step is to evaluate the risks of the substrates, reagents, reaction intermediates, reaction products, solvents and catalysts and other auxiliary agents used in the reaction, as well as the risks that may arise after their interaction
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For example, if there is risk of explosive, toxic if there is, whether the corrosive, irritating if, like whether sensitization
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It is not only necessary to analyze the hazard from the overall structural characteristics of the compound, but also from the structure of the functional group to which the organic compound belongs, because the active functional group of most organic compounds determines its chemical and physical properties.
This is chemical The basic law
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Through the type of active functional group and its location, it can be qualitatively judged whether there are violent side reactions such as polymerization and decomposition, whether it is explosive, toxic, corrosive, irritating and sensitizing, and whether there is gas generation
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These issues will not be introduced in detail in the general literature.
Even if mainstream literature such as MSDS and OS is generally believed to be reliable, it will be limited by the author’s knowledge level, changes and advances in science and technology, and what Limited by conditions such as investigation and practice, some real danger warning descriptions will be missed, so these materials can only be used for reference, and cannot be blindly believed or copied blindly
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(2) Evaluate the heat change at the beginning of the reaction, during the reaction, the end of the reaction, and the post-processing of the reaction, and whether there are risk factors such as the temperature critical value closely related to the reaction rate and the reaction temperature.
If necessary, use a calorimeter such as DSC.
Perform reaction heat measurement
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(3) Assess whether the safe capacity and safe space of the reaction are sufficient
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(4) Assess whether the reaction conditions are harsh and whether it can be carried out in a more gentle way to reduce the risk to a breeze.
(5) Evaluate the requirements for the instruments and equipment of the various hazards in the reaction, and whether they can be flexible and replaced to turn the danger into safety
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(6) Assess the relationship between the scale of the reaction and the risk
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(7) Assess whether it can be changed to other safer raw materials, synthetic processes, operations, and equipment
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(8) Assess other possible risks
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