Rhubarb

Rhubarb is used traditionally as both a laxative and an antidiarrheal agent (see Chapter 57). 

Botanically, rhubarb (Rheum rhaponticum) is a vegetable not a fruit. It was originally cultivated some 2000 years ago in Northern Asia as a medicinal and ornamental plant. It is 

Samples Total antioxidant capacity Total phenolic content  

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Crystallizes from water in large colourless prisms containing 2H2O. It is poisonous, causing paralysis of the nervous system m.p. 101 C (hydrate), 189°C (anhydrous), sublimes 157°C. It occurs as the free acid in beet leaves, and as potassium hydrogen oxalate in wood sorrel and rhubarb. Commercially, oxalic acid is made from sodium methanoate. This is obtained from anhydrous NaOH with CO at 150-200°C and 7-10 atm. At lower pressure sodium oxalate formed from the sodium salt the acid is readily liberated by sulphuric acid. Oxalic acid is also obtained as a by-product in the manufacture of citric acid and by the oxidation of carbohydrates with nitric acid in presence of V2O5. 

A balanced chemical reaction indicates the quantitative relationships between the moles of reactants and products. These stoichiometric relationships provide the basis for many analytical calculations. Consider, for example, the problem of determining the amount of oxalic acid, H2C2O4, in rhubarb. One method for this analysis uses the following reaction in which we oxidize oxalic acid to CO2. 

The amount of oxalic acid in a sample of rhubarb was determined by reacting with Fe as outlined in reaction 2.2. In a typical analysis, the oxalic acid in 10.62 g of rhubarb was extracted with a suitable solvent. The complete oxidation of the oxalic acid to CO2 required 36.44 mb of 0.0130 M Fe. What is the weight percent of oxalic acid in the sample of rhubarb ... 

Of nutrient chelates in the human diet, oxalates and phytates are the most common. OxaUc acid (8), found principally in spinach, rhubarb leaves, beet leaves, some fmits, and mushrooms, is a primary chelator of calcium. Oxalate present in pineapple, kiwifmit, and possibly in other foods, occurs as calcium... 

The potassium or calcium salt form of oxaUc acid is distributed widely ia the plant kingdom. Its name is derived from the Greek o>ys, meaning sharp or acidic, referring to the acidity common ia the foflage of certain plants (notably Oxalis and Mmex) from which it was first isolated. Other plants ia which oxahc acid is found are spinach, rhubarb, etc. Oxahc acid is a product of metabohsm of fungi or bacteria and also occurs ia human and animal urine the calcium salt is a principal constituent of kidney stones. 

Enhancers and Inducers. A sweetness enhancer is defined as a compound that imparts no taste per se, but when combined with a sweetener in small quantities, increases sweetness intensity. A tme sweetness enhancer has yet to be found. However, a good sweetness inducer, miraculin [143403-94-5] or [125267-18-7] (124), is known. Miraculin is a glycoprotein found in the fmit (called Miracle Fmit) of a West African shmb, chardella dulcifica. By itself, miraculin imparts no sweetness. When activated in the mouth by acidic substances, however, a sucrose-like sweetness is perceived. Thus, sour lemon, lime, grapefmit, rhubarb, and strawberry taste sweet when combined with miraculin. The taste conversion effect can last an hour or longer. 

KInder-balsam, m. soothing sirup, -emah-rung, /. infant feeding child nutrition, -iahmung, / infantile paralysis, -mehl, n. (powdered) infant food, -nahrmittei, n. infant food, -pech, n. meconium, -pulver, n. (Pharm.) compound powder of rhubarb, -schleim, m., -schmiere, /. vernix caseosa. -seife, /. nursery soap. 

Rhabarbert m. rhubarb. — falscher—, (Pharm.) the root of European rhubarb. 

Oxalic acid, H2C204, is a poisonous compound found in rhubarb leaves. Draw the Lewis structure for oxalic acid. There is a single bond between the two carbon atoms, each hydrogen atom is bonded to an oxygen atom, and each carbon is bonded to two oxygen atoms. 

Self-Test F.5B The molar mass of oxalic acid, an acid present in rhubarb, is 90.0 g-mol , and its empirical formula is CH02. What is its molecular formula ... 

Vegetables also contain carboxylic acids that contribute to their flavors. One example is oxalic acid, prevalent in spinach and rhubarb. Raw rhubarb leaves are mildly poisonous, and folklore holds that the toxic substance is oxalic acid. However, raw spinach can be eaten safely despite its equally high content of this acid. 

C17-0116. Oxalic acid, a diprotic carboxylic acid found in many plants, including rhubarb, is an effective stain remover. Consider the following diagram to be a small section of an aqueous solution of oxalic acid ... 

Ecstasy (Adam, brownies, burgers, Dennis the Menace, disco biscuits, doves, E, Edward, essence, fantasy, love doves, M and Ms, New Yorkers, rhubarb and custard, shamrocks, white doves, X, XTC) is an illegally manufactured drug that comes in tablet or capsule form. The appearance varies considerably ranging from brown, white or pink tablets to yellow, clear, red and black or red and yellow capsules, often with pictures, designs or logos. It is taken orally. 

Did we but know the mechanical affections of the particles of rhubarb, hemlock, opium and a man, as a watchmaker does those of a watch,. .. we should be able to tell beforehand that rhubarb will purge, hemlock kill and opium make a man sleep. 

Oztiirk M, Aydogmus-OzUirk F, Dura ME and Topcu G. 2007. Antioxidant activity of stem and root extracts of rhubarb (Rheum ribes) an edible medicinal plant. Food Chem 103(2) 623-630. 

Calcium oxalate (723) occurs as the monohydrate (whewellite, the thermodynamically stable form under ambient conditions (724)), the dihydrate (weddellite) in plant calcium stores and in sap, or the trihydrate (725). Calcium oxalate also plays a structural role in plants. Oxalate, for example from excessive amounts of rhubarb or spinach, inhibits absorption of Ca2+ from the GIT precipitation of calcium oxalate is the reason for the toxicity of oxalates. Calcium oxalate may also occur in man, where it can appear as minute star-shaped crystals in the urine. It is the main constituent of the majority of urinary calculi in man (726,727). The relationships between dietary calcium... 

Tuba et al. (24) reported that rats fed 15.4% dried rhubarb or an equivalent amount of sodium oxalate grew at a slower rate and had higher serum alkaline phosphatase levels than rats fed control diets containing calcium lactate. The calcium lactate diets contained either 0.5% or 0.09% calcium. The rhubarb and sodium oxalate diets contained 0.5% calcium and 0.95% oxalate. 

In the studies on rats, the amounts of spinach, cocoa, rhubarb, or oxalate salts fed were much higher than would normally be included in diets. The levels of calcium and vitamin D were generally low. 

O Oxalic acid, HOOCCOOH, is a weak diprotic acid that occurs naturally in some foods, including rhubarb. Calculate the pH of a solution of oxalic acid that is prepared by dissolving 2.5 g in 1.0 L of water. What is the concentration of hydrogen oxalate, HOOCCOO , in the solution ... 

This carboxylic acid is found in the leaves of rhubarb. Its lUPAC name is ethanedioic acid. 

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