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Anaranjado de Metilo

The document provides a procedure for synthesizing methyl orange through a diazotization reaction of sulfanilic acid followed by coupling with dimethylaniline. The 11 step procedure involves (1) preparing the diazonium salt of sulfanilic acid, (2) adding this to a solution of dimethylaniline to form the dye helianthin, (3) basifying the solution to produce methyl orange salt, and (4) purifying the product through recrystallization and filtration. The final two steps instruct obtaining an NMR spectrum of the product and assigning all peaks in the spectrum.

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62 views2 pages

Anaranjado de Metilo

The document provides a procedure for synthesizing methyl orange through a diazotization reaction of sulfanilic acid followed by coupling with dimethylaniline. The 11 step procedure involves (1) preparing the diazonium salt of sulfanilic acid, (2) adding this to a solution of dimethylaniline to form the dye helianthin, (3) basifying the solution to produce methyl orange salt, and (4) purifying the product through recrystallization and filtration. The final two steps instruct obtaining an NMR spectrum of the product and assigning all peaks in the spectrum.

Uploaded by

Luis Gb
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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P age |6

Procedure

Diazotized Sulfanilic Acid

1. Dissolve 0.29 g of anhydrous sodium carbonate in 12.5 mL of water. Use a


50 mL Erlenmeyer flask.

2. Add 1.0 g of sulfanilic acid monohydrate to the solution and heat it until it
dissolves. A small amount of suspended material may render the solution cloudy.

3. Gravity-filter the still hot solution and rinse the used filter paper with a little (0.5 -
1.0 mL) hot water.

4. Cool the filtrate to room temperature, add 0.375 g of sodium nitrite, and stir
until solution is complete.

5. Pour this mixture, while stirring, into a 100-mL beaker containing 8 mL of ice
water to which 1.25 mL of concentrated hydrochloric acid have been added; add
the HCl dropwise to maintain a temperature of 0-5oC. The diazonium salt of
sulfanilic acid should soon separate as a finely divided white precipitate. Keep
this suspension cooled in an ice bath until it is to be used.

Methyl Orange

6. In a test tube, mix together 0.7 mL of dimethylaniline and 0.5 mL of glacial acetic
acid.

7. Add this solution dropwise to the cooled suspension of diazotized sulfanilic acid
in the 100-mL beaker. Stir the mixture vigorously. In a few minutes, a red
precipitate of helianthin should form. Keep the mixture cooled in an ice bath for
about 15 minutes to ensure completion of the coupling reaction.

8. Add 7.5 mL of a 10% aqueous sodium hydroxide (NaOH) solution. Do this


slowly and with stirring, as you continue to cool the beaker in an ice bath. Check
with litmus or pH paper to make sure the solution is basic. If it is not, add more
base.

9. Heat the mixture to boiling with a Bunsen burner for 10 to 15 minutes to dissolve
most of the newly formed methyl orange. When all (or most of it) the dye is
dissolved, add 2.5 g of sodium chloride, and cool the mixture in an ice bath. The
methyl orange should recrystallize. Filter using a Buchner funnel.
P age |7

10. To purify the product, transfer the filter cake and paper to a large beaker
containing about 40 mL of boiling water. Maintain the solution at a gentle boil for
a few minutes, stirring it constantly.
Note: Not all the dye will dissolve, but the salts with which it is contaminated will
dissolve.

11. Remove the filter paper and allow the solution to cool to room temperature. Cool
the mixture in an ice bath, and when it is cold, collect the product by vacuum
filtration, using a Buchner funnel. Allow the product to dry, weight it, and
calculate the percentage yield.
Note: The product is a salt. Since salts do not generally have well-defined melting
points, the melting-point determination should not be attempted.

Spectroscopy

1. Obtain a NMR spectrum of the product. Consult with your laboratory instructor
about how to do this.

2. Assign all the NMR peaks in the spectrum.

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