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Chapter 23: Question 23.42 (page 1240)

Cellulose is converted to cellulose acetateby treatment with acetic anhydride and pyridine. Cellulose acetate is soluble in common organic solvents, and it is easily dissolved and spun into fibers. Show the structure of cellulose acetate.

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Cellulose acetate

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01

Cellulose acetate

Cellulose acetate is a cellulose derivative and a biodegradable material. It is partially acetylated cellulose in which acetyl content ranges from mono to triacetate groups. Cellulose is converted to cellulose acetate by treatment with acetic anhydride and pyridine.

02

Structure of cellulose acetate

The most common form of cellulose acetate possesses acetate groups on two of every three hydroxyls of anhydroglucose unit. The anhydroglucose unit is the repeating cellulose unit with three hydroxyl groups that react and get converted to acetate esters. It is soluble in organic solvents.

The structure of Cellulose acetate

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Most popular questions from this chapter

Except for the Tollens test, basic aqueous conditions are generally avoided with sugars because they lead to fast isomerizations.

  1. Under basic conditions, the proton alpha to the aldehyde (or ketone) carbonyl group is reversibly removed, and the resulting enolate ion is no longer asymmetric. Reprotonation can occur on either face of the enolate, giving either the original structure or its epimer. Because a mixture of epimer results, this process is called epimerization. Propose a mechanism for the base-catalyzed equilibration of glucose to a mixture of glucose and its C2 epimer, mannose.
  2. Propose a mechanism for the isomerization of a ketose to an aldose, via the enediol intermediate, shown immediately above. Note that the enediol has twoprotons and removing one or the other gives two different enolate ions.

An important protecting group developed specifically for polyhydroxy compounds like nucleosides is the tetraisopropyl-disiloxanyl group, abbreviated TIPDS, that can protect two alcohol groups in a molecule.

(a) The TIPDS group is somewhat hindered around the Siatoms by the isopropyl groups. Which OHis more likely to react first with TIPDS chloride? Show the product with the TIPDS group on one oxygen.

(b) Once the TIPDS group is attached at the first oxygen, it reaches around to the next closest oxygen. Show the final product with two oxygens protected.

(c) The unprotected hydroxy group can now undergo reactions without affecting the protected oxygens. Show the product after the protected nucleoside from (b) is treated with tosyl chloride and pyridine, followed by NaBr, ending with deprotection with Bu4NF.

Is gentiobiose a reducing sugar? Does it mutarotate? Explain your reasoning.

Draw the structures of the compounds named in Problem 23-20 parts (a), (c), and (d). Allose is the C3 epimer of glucose and ribose is the C2 epimer of arabinose.

After a series of Kiliani鈥揊ischer syntheses on (+)-glyceraldehyde, an unknown sugar is isolated from the reaction mixture. The following experimental information is obtained:

(1) Molecular formula C6H12O6

(2) Undergoes mutarotation.

(3) Reacts with bromine water to give an aldonic acid.

(4) Reacts with HNO3 to give an optically active aldaric acid.

(5) Ruff degradation followed by HNO3 oxidation gives an optically inactive aldaric acid. (6) Two Ruff degradations followed by HNO3 oxidation give meso-tartaric acid.

(7) When the original sugar is treated with CH3I and Ag2O, a pentamethyl derivative is formed. Hydrolysis gives a tetramethyl derivative with a free hydroxy group on C5.

(a) Draw a Fischer projection for the open-chain form of this unknown sugar. Use Figure 23-3 to name the sugar.

(b) Draw the most stable conform

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