Dehydration

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dehydration

[‚dē·hī′drā·shən]
(chemistry)
Removal of water from any substance.
(organic chemistry)
An elimination reaction in which a molecule loses both a hydroxyl group (OH) and a hydrogen atom (H) that was bonded to an adjacent carbon.

Dehydration

 

splitting off of water from organic or inorganic compounds. Dehydration can be achieved thermally (mostly in the presence of catalysts) or chemically by the action of dehydrating agents (water-binding substances). The formation of ethylene from ethyl alcohol is an example of dehydration performed by passing ethyl alcohol through a tube containing aluminum oxide (catalyst) at 300°–400°C or by heating it with concentrated sulfuric acid (dehydrating agent) to 170°C:

CH3 —CH2OH → CH2 ═CH2 + H2O

The formation of ethylene is an example of intramolecular dehydration. However, heating the excess of ethyl alcohol with sulfuric acid to 140°C leads mainly to intermolecular dehydration with the resulting formation of diethyl ether:

CH3CH2 —O—H + H—O—CH2CH3 → CH3CH2 —O—CH2CH3 + H2O

Intramolecular dehydration of acetic acid CH3COOH yields ketene CH2=C=O, whereas the intermolecular dehydration of acetic acid yields acetic anhydride (CH3CO)2O. Dehydration of the amides CH3CONH2 yields nitriles CH3C≡N. Formation of nitrogen pentoxide from nitric acid in the presence of phosphorus pentoxide is an example of the dehydration of an inorganic substance:

Dehydration also includes the processes leading to the removal of water of crystallization from crystal hydrates and the removal of water bound by adsorption forces. Dehydration is the opposite of hydration.

B. L. DIATKIN


Dehydration

 

loss of water by an organism to a point below the physiological norm. Animals die when they lose 20–25 percent of their body water, and disorders arise when the water loss reaches 10 percent. Dehydration may develop as a result of excessive water loss (repeated vomiting, diarrhea, excessive perspiration, extensive burns) or restriction of water intake.

Excessive water loss leads to hypo-osmolar dehydration, a condition in which the body loses a significant quantity of electrolytes along with the excreted fluids, the osmotic pressure in the cells is higher than in the interstices of tissues, and fluid enters the cells. When the water intake is restricted, the loss of fluid substantially exceeds the loss of electrolytes. This leads to hyperosmolar dehydration, a condition in which the osmotic pressure in the interstices of tissues increases and water passes from the cells to the extracellular space, as a result of which the cells become dehydrated and die.

Dehydration is accompanied by agonizing thirst, which is more difficult to endure than the hunger caused by deprivation of food. The secretion of all digestive glands is reduced, the blood thickens, and the blood viscosity increases. The changes in the blood lead to serious disorders of blood circulation and to disruption of renal function. Acute dehydration may lead to mental disorders, collapse, and sometimes death. Dehydration develops considerably more rapidly in children than in adults, since in children, especially infants, the amount of water excreted through the kidneys, skin, and lungs per unit of body surface is far greater than in adults. In pathological conditions causing hypo-osmolar dehydration, thirst should be quenched by drinking salted water to compensate not only for the water loss but the loss of electrolytes as well. Treatment consists in removing the primary cause of dehydration.

G. A. DROZDOVA

dehydration

The removal of water vapor from air by the use of absorbing or adsorbing materials.
References in periodicals archive ?
One can be acutely dehydrated, such as after a long endurance event, or chronically dehydrated after losing small amounts of water over a long period of time.
The situation is different for dehydrated (mainly hot-air dried) fruit, and tropical fruit in particular.
Substrates were dehydrated by heating in TABULAR DATA OMITTED a tube furnace at 1000 |degrees~ C for 10 hrs under a constant flow of compressed air or nitrogen; the air was filtered for organics and dried before use.
By virtue of this, Nissin ranks second in overall dehydrated soup sales, outsold only by Lipton, which claims an estimated 32% market share.
It helps to mention another great product that aids other dehydrated parts of the body.
The dehydrated mixture of fish and spinach cakes were prepared at the Fish Technology Laboratory of the Iguatemi Experimental Farm, Universidade Estadual de Maringa, Maringa, State of Parana, Brazil.
Old Fashioned Chicken Noodle Soup Mix 1/4 cup dehydrated carrots 1/4 cup dehydrated celery 1/4 cup dehydrated onion 1/2 cup dehydrated butter 1 teaspoon chicken bouillon 1 cup wide egg noodles 1/2 teaspoon pepper Add 1 cup chicken, 8 cups of water, and mix to a large pot.
He was so dehydrated he was grabbing tissues used to cool his head and sucking the fluid.
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The results showed that the cheap dehydrated carbon from date palm leaflets proves to be as efficient as activated carbon for removing pharmaceuticals and dyes.
If you are well hydrated your urine should be a pale shade similar to the colour of champagne, if you are dehydrated your urine will tend to be much darker.
To increase yield and improve profitability for its dehydrated soups and sauces, the Unilever Bestfoods Knorr site at Duppigheim in Alsace is adding the lighter weight ingredients to each mix via Ishida's specialist Tilliput' weigher, the world's smallest mulithead weigher, rather than (he volumetric dosing previously used.