Question

1. Based on rhe amount of reagents, which reagent is the limiting reagent.

2. what is the struckture of B-alanine

1. Based on the amounts of reagents used in this experiment, which reagent is the limiting reagent? What is the theoretical yield (in grams) of trans-4-methoxycinnamic acid? Show all of your work. (Hint: Solvents and catalysts cannot be a limiting reagent) 2. Write a complete curved arrow mechanism for the first phase involved in the synthesis of Ho он CHyo pyridine CH 0 он Phase I several steps он 3. B-alanine has been suggested to have several important roles in synthesis of trans 4- methoxycinnamic acid. One is to activate the aldehyde carbonyl through the formation of an imine; another is to act as a buffer to assist in the malonic acid deprotonation a.) What is the structure of p-alanine? b.) What is the structure of the imine formed between β-alanine and 4-methoxy- benzaldehyde? c) What is a buffer? How can β-alanine serve this role in the reaction? why is a buffer necessary? 242 Sunscreen. он но OH -CO2 он H20 CH30 β-alanine pyridine CH30 CH30 Experimental Procedure: Reagent Table: to be included in your notebook and completed while performing the experiment. Reagent Molecular Mass Moles Volume Density Weight(g) (g/mL) 4-methoxy- benzaldehyde 1.119 β-alanine | 8909 malonic acid 104.06 79.10 pyridine 0.978 To a 25 mL round bottom flask equipped with a stir bar, add 804 μL of 4-methoxybenzaldehyde, 0.100 g of B-alanine, and 1.75 g of malonic acid. In the fume hood, add 3 ml. of pyridine. Attach a condenser and heat the mixture under reflux for 90 minutes, using a Thermowell as a heat source. Remove the flask from the heat source and allow it to cool to room temperature. Cool further in an ice bath for 10 minutes. Slowly and carefully add 8 mL. of concentrated HCI (in 2 ml. portions) to the flask. At this time a white precipitate should form. Collect the product by vacuum filtration and wash the crystals with ice cold water (2 x 10 mL). Leave the solid under vacuum for 10 minutes to assist drying Carefully remove the filter paper from the Buchner funnel and place it on a watch glass. Allow the crystals to dry until the next laboratory period.

Answer 1

1.) Firstly calculate no.of moles of each reactant :

Structure of bcta-alaninc NH2 beta-alanine Imine formation of alanine and aldehyde но beca-alanine4-methoxybenzaldehyde mine Mechanism он он но Me Co2 -H2o

4-methoxy benzaldehyde : density =mass/volume, therefore mass =0.89 ;

no of moles = mass/mol.wt = 0.89/136.15 = 0.0065 ; limiting reagent = 0.0065/136.15 = 0.88

Malonic acid = 1.75/104.06 = 0.0168 ; limiting reagent = 1.74

Beta-alanine = 0.1/89.09 = 0.0011 ; limiting reagent = 0.097

Pyridine = 2.9/79.10 = 0.037 ; limiting reagent = 2.92

Limiting reagent is the compound that is consumed completely in the reaction. It can be calculated by dividing no.of moles of each by its mol.wt. The reactant that has smallest number of moles is limiting reagent. So in the above experiment 4-methoxy benzaldehyde is limiting reagent.

for one mole of aldehyde,one mole of cinnamic acid is used,so there are 0.0065 moles of acid same as aldehyde

molecular mass of acid = 178.1

therefore,178.1g/mol * 0.0065mol = 1.15g

Theoretical yield = 1.15g

2.) Structure of beta-alanine : look at attachment

3.) Buffer: it is solution which maintains its pH to near constant even upon addition of aid or base.

It acts both as bronsted acid as well as bronsted base due to presence of amino and acid functional group.

Buffer is necessary in reaction to moderate changes in solution pH. it helps to maintain the equilibrium.