W4/4/18 CH 4521-9: Combinatorial Synthesis of Azo Dyes Combinatorial chemistry a
ID: 1041794 • Letter: W
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W4/4/18 CH 4521-9: Combinatorial Synthesis of Azo Dyes Combinatorial chemistry allows chemists to prepare a large number of structurally similar compounds efficiently. The concept slightly different reactants to make a "library" of possibleproducts combinatorial chemistry s to use Identical reaction conditions, but start with The combinatorial approach will be used in this experiment to synthesize a variety of azo dyes. Azo dyes are compounds that contain the functional group R-N N-R' where R and R' can either by an alkyl group or an any group. The R-NaN-R group is called an azo group from the Greek word for nitrogen. The more stable derivatives contain two aryl groups and that is what well be using for today's experiment Aryl azo compounds have vivid colors of red,yellow and grange because of the pi-delocalization. These compounds are used as dyes. Some, such as methyl orange, are used as acid-base Indicators since they change color based on pH. Many of them are used in the dye industry and they are important commercialy The azo coupling reaction is an organic reaction between a diazonium compound and an aniline, phenol or other aromatic compound. The diazonium salt acts as an electrophile and the activated arene is the nucleophile. The reaction s an electrophilic aromatic substitution reaction. The product is typically also aromatic and will absorb longer wavelengths of lignt because of the increased conjugation. An example of the azo coupling reaction is shown below N C HC The product produced is primarily the trans isomer, although conversion to the cis can occur upon photolysis. For this experiment, individual groups will be assigned a unique starting material. Each gr azo coupling reaction and create a different azo dye product. Fabric strips will be dyed with the products and the fabric strips compared. Any conclusions that are reached concerning the structure of the final product and the color of the dyed strips should be discussed in the final lab report. The first experiment focuses on an azo coupling reaction with an aminobenzenesulfonic acid (either ortho meto- or para-).This reactant is coupled with an aromatic reactant (1-haphthol, 2-haphthol, salicylic acid or8- anilino-1-naphthalenesulfonic acid ammonium salit The second experiment focuses on the azo coupling reaction of 4-nitroaniline with one of the aromatic reactants: 1-naphthol, 2-naphthol, salicylic acid or 8-anilino-1 2-naphthol, salicylic acid or 8-anilino-1-naphthalenesulfonic acid ammonium saltExplanation / Answer
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To find out the theoretical yield and percentage yield, first we have to determine the limiting reagent. In a chemical reaction the limiting reagent is the one which is present in lower quantities, thereby they will determine how much of the products are made.
1) identify the limiting reagent
Quantity of 4- nitroaniline taken = 0.7 g
MW of 4- nitroaniline = 138.12g/mol
Number of moles of 4- nitroaniline= quantity taken / MW
=0.7g/ 138.12g/mol
= 0.005068 Mols
= 5.068 mmols
Number of mmols of aromatic coupling reagent = 5.1 mmols
Therefore, the limiting reagent present in the reaction between 4- nitroaniline and aromatic coupling reagent is 4- nitroaniline.
4- nitroaniline (5.068mmol) + aromatic coupling reagent (5.1 mmol)-----> azodye ( 5.068 mmol)
Theoretical yield in mmols= 5.068 mmols
Theoretical yield in grams= 5.068 mmols of azodye * the molecular weight of the azodye = 5.068 mmols* 293.29 g/mol
=1.4864 gms
This will be the maximum amount of product that can be obtained during a chemical reaction but in actual practice the quantity will be less,
because the loss of product usually occurs during isolation and purification. Thus yield is expressed in terms of percentage yield .
it is given as
Percentage yield= (actual yield / theoretical yield) * 100%
= ( quantity obtained/ 1.4864) * 100%
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