Synthesis of Dulcin Objective: The main objective of this lab is to gain experience at a typical synthesis and semi-microscale recrystallization. Discussion Questions: 1) How fast should the temperature be raised when determining a melting point? When can the temperature be raised more quickly? 2) If there is an Impurity present in a sample, what is the effect on the melting point? 3) Explain why a) salt, spread on roads in the winter, helps prevent icing in, for instance, southern Ontario, and b) salt is useless on the much colder roads of Manitoba. ) You would have to slowly raise the temperature up when determining the melting point due to the sensitivity of the dulcin being able to change from solid to liquid at any point. If the temperature is set to high to fast it is possible to miss the change of state and not be able to record the time which is why it should originally be set pretty slow. If set high too fast it will melt faster causing the melting point to be inaccurate. As soon as you get the general idea of when change in state will occur, that is when you can probably raise the temperature more quickly. ) If there are impurities present in the sample it can cause many problems, it can lower or raise the boiling point due to it having an effect on the dulcin itself. Basically it will increase the range of the boiling and melting points, which will give an inaccurate reading. If the dulcin were to be fully pure the range would have a difference of maybe 1 to 2, having an impurity would make a huge difference. 3) Salt is sprinkled on the streets so that when it mixes with the moisture and the water it creates a saline mixture.
This mixture has a lower freezing point then normal water does so that means it would only freeze at lower temperatures. This basically prolongs the icing process and basically can fully prevent ice from forming on the roads. On older colder roads of Manitoba it reaches the colder temperatures necessary to freeze over the saline mixture which ends up making it useless to do. Conclusion: Yield: To calculate you must take the amount of crude dulcin you started with and have it divided by the pure dulcin then multiply it by 100 to get a %. Pure Dulcin: 0. 6168g Crude Dulcin: 1. 2356g Melting point of crude: 167-171
Melting point of pure: 174-176 The recrystallization process is one that has been tested multiple times and been proven effective in many experiments. In our experiment I would have to say that it was a very effective process due to the melting points that we were able to get with our products. The melting point for the crude substance was between 167 and 171 . This shows that the crude definitely had some impurities in it keeping it a bit away form the theoretical melting point. The melting point of our pure substance was between 174and 176 which is actually extremely close to the theoretical melting point.
This shows us that the recrystallization process does an extremely good job, even though it takes a lot of time and effort to do it. There way be some flaws with it and some error that can come about with how the apparatus is set up or how the students take care of the products. In the end it is a great process and if the technique is done properly and precisely the effectiveness off this process is very high and produces great results. Reference: “University of Winnipeg CHEM-2202/3 Organic Chemistry I Lab Manual Fall 2012”