Preparation of benzopinacol from benzophenone. 2. Preparation of Benzopinacol via Photoreduction of ... Pages 1 2022-11-04
Preparation of benzopinacol from benzophenone Rating:
Benzopinacol, also known as benzopinacolone, is an organic compound that can be prepared from the starting material benzophenone through a series of chemical reactions. The synthesis of benzopinacol from benzophenone involves several steps, including the formation of a Grignard reagent, the conversion of the Grignard reagent to a ketone, and the reduction of the ketone to the final product. In this essay, we will outline the preparation of benzopinacol from benzophenone, including the necessary reagents, conditions, and mechanisms of each step.
The first step in the synthesis of benzopinacol is the formation of a Grignard reagent. Grignard reagents are a type of organometallic compound that are formed by the reaction of an alkyl or aryl halide with magnesium metal in an ether solvent. To prepare the Grignard reagent, benzophenone is dissolved in an ether solvent and cooled to a low temperature. Magnesium metal is then added to the solution, and the mixture is stirred until the magnesium has completely reacted with the benzophenone.
Once the Grignard reagent has been formed, it is converted to a ketone through the addition of a halogenated hydrocarbon, such as carbon tetrachloride or chloroform. The ketone is then reduced to the final product, benzopinacol, through the addition of a reducing agent, such as lithium aluminum hydride or sodium borohydride.
The mechanism of the Grignard reaction involves the formation of a complex between the magnesium and the halogen atom of the alkyl or aryl halide. The complex then undergoes a nucleophilic attack on the carbon atom of the halide, forming a carbon-magnesium bond and a halide ion. The resulting Grignard reagent is a nucleophile that can attack electrophilic carbon atoms, such as those found in aldehydes and ketones.
In the case of the synthesis of benzopinacol from benzophenone, the Grignard reagent attacks the electrophilic carbon atom of the benzophenone, forming a carbon-magnesium bond and a phenoxide ion. The phenoxide ion is then protonated by the halogenated hydrocarbon, forming a ketone. The ketone is then reduced to the final product, benzopinacol, through the addition of a reducing agent.
In conclusion, the synthesis of benzopinacol from benzophenone involves the formation of a Grignard reagent, the conversion of the Grignard reagent to a ketone, and the reduction of the ketone to the final product. This synthesis involves several steps and requires the use of various reagents and conditions, but it is a valuable method for the preparation of benzopinacol, which has a wide range of applications in organic chemistry.
2. Preparation of Benzopinacol via Photoreduction of ... Pages 1
Prelab Questions Use online or other sources to answer the following questions prior to laboratory. Allow the solid to air dry. Organic chemists are interested inphotochemical preparations of molecules since light can act as a catalyst orreactant , causing interesting reactions to occur. Procedure Place 2 g benzophenone into a 20 mL vial and add about 10 mL 2-propanol. In order to achieve complete dissolution, gentle heating in a water bath is required. Place the vial in the windowsill in such as waythat it will be exposed to as much light as possible.
Weigh the remaining amount of solid and then recrystallize by dissolving in a minimum amount of methylene chloride and adding petroleum ether until the solution becomes cloudy. Determine the mass in milligrams of product expected. Include the mechanism for the reaction. It is important that the solution not come into direct contact with the rubber as it may leach out some compounds which can quench benzophenone excited states. After the solidis dissolved, add 1 drop glacial 100% acetic acid, then fill the vial with2-propanol until it is a little more than half way into the screw neck of the vial.
After the crystals dry on an open watch glass, determine theirmass and melting point. References 1 Durst, T. Dissolve the solid with gentle warming in a warm water bath. Thisparticular reaction is not catalyzed by light; rather, it is driven by light. When thevial is inverted, if more than a small bubble of air is present, reopen thevial and add a little more 2-propanol.
Put a strip of lab tape on the top of the vial with your name, the date, andthe name of this laboratory. Reacquire analytical data for the recrystallized sample as described in Step 5. For example, we havepreviously discussed the use of ultraviolet light as a catalyst for theformation of radicals in the halogenation of alkanes. Take the melting point, infrared spectrum and 1H NMR spectrum of your sample, an authentic sample of benzopinacol, and that of the starting material, benzophenone. Tightlyfasten the cap and invert the vial several times to mix the liquid.
Photochemical preparation of benzopinacol Photochemical Reactions Preparation of Benzopinacol Purpose Photochemistry is the study of the chemical interactions which occur whenmolecules interact with light. The light is needed in this reaction to break the π bond between the carbonand oxygen in the carbonyl group of benzophenone forming a diradical. Using density and molecular weight, determine the number of millimoles of 2-propanol used. Of thebonds in the two reactants, this bond is weakest making it most susceptible to theenergy provided by the ultraviolet light. Eventually one benzhydrol radical will collide with anotherleading to the formation of the final stable product.
In this step the diradical becomes abenzhydrol radical, while the solvent molecule becomes a new radical. Why must the test tube be tightly stoppered during irradiation? What would you expect to occur if the test tube were not stoppered? Why are they not isolated? Propose a reaction for the preparation of benzopinacol from benzophenone which does not involve photochemistry. Weigh the solid and determine the percent yield for the reaction. Collect the solid by suction filtration and wash with 1 mL of cold 2- propanol. In this laboratory, wewill use ultraviolet light from sunshine to promote a radical reaction.
Allow the solution to cool to room temperature, then cool in an ice-bath. In other words, we can think of photons of light as being a neededreactant in this process. Why are you asked to "take care not to wrapParafilm around the main body of the vial? Find a literature melting point for the product, benzopinacol Include reference to source. After the irradiation, cool the test tube in an ice-bath to precipitate more of the solid. Prepare a solution of benzophenone 0. After the diradical forms it immediately becomes a scavenger, its oxygen atomquickly finding a relatively easily removed hydrogen in the 2° position inthe plentiful solvent molecules.
Data AnalysisExamine the analytical data obtained for your crude and recrystallized sampleand compare them to those of an authentic sample of benzopinacol andbenzophenone to confirm its identity as benzopinacol and to determine its purity. Next week, harvest the product crystals which form by pouring off the liquid organic waste container and scraping the crystals from the vial with aspatula. Using molecular weight, determine the number of millimoles of benzophenone used. What photoproducts other than benzopinacol would you expect to form during the photolysis? Wrap the cap with a small strip of Parafilm to avoid any leakage, taking carenot to wrap Parafilm around the main body of the vial. Place the test tube in the Luzchem photoreactor using all 10 lamps and irradiate until the amount of solid which has precipitated from solution does not change 2. This newly formed radical is now highly reactive, enabling it to offer ahydrogen atom to the oxygen of another benzophenone diradical, thus resultingin the formation of a stable molecule, acetone, as well as another benzhydrol radical.