Applications
As a metallurgical
flux
Zinc chloride has the
ability to attack metal oxides (MO) to give derivatives of the formula
MZnOCl2. This reaction is relevant to the utility of
Zinc chloride as a flux for
soldering - it dissolves oxide coatings exposing the
clean metal surface. Typically this flux was prepared by dissolving zinc
foil in dilute hydrochloric acid until the liquid ceased to evolve hydrogen; for this reason, such flux was
once known as killed spirits.
Because of its corrosive nature, this flux is not suitable for
situations where any residue cannot be cleaned away, such as electronic
work. This property also leads to its use in the manufacture of
magnesia cements for dental fillings and certain mouthwashes as an active ingredient.
In
organic synthesis
In the laboratory, Zinc chloride finds wide use, principally
as a moderate-strength Lewis acid. It can
catalyze (A) the Fischer
indole synthesis, and
also (B) Friedel-Crafts
acylation reactions
involving activated aromatic rings.
Related to the latter is the classical preparation of
the dye fluorescein
from phthalic anhydride
and resorcinol, which involves a
Friedel-Crafts
acylation. This transformation has in fact been
accomplished using even the hydrated ZnCl2.
Hydrochloric acid alone reacts poorly with
primary alcohols and secondary alcohols,
but a combination of HCl with
ZnCl2
(known together as the "Lucas reagent") is
effective for the preparation of alkyl chlorides. Typical reactions are
conducted at 130 °C. This reaction probably proceeds via an SN2
mechanism with primary alcohols but SN1
pathway with secondary alcohols.
Zinc chloride also activates
benzylic and
allylic halides towards
substitution by weak nucleophiles
such as alkenes:
In similar fashion, Zinc chloride
promotes selective NaBH3CN reduction of tertiary,
allylic or benzylic
halides to the corresponding hydrocarbons.
Zinc chloride is also a useful starting reagent for
the synthesis of many organozinc
reagents, such as those used in the palladium catalyzed
Negishi coupling with
aryl halides or vinyl halides. In
such cases the organozinc compound is
usually prepared by transmetallation
from an organolithium
or a Grignard reagent.Zinc
enolates, prepared
from alkali metal enolates and Zinc
chloride, provide control of
stereochemistry in
aldol condensation reactions due to
chelation on to the zinc.
The threo product was favored over the
erythro by a factor of 5:1 when Zinc
chloride in DME/ether
was used. The chelate is more stable when
the bulky phenyl group is pseudo-equatorial
rather than pseudo-axial, i.e.,
threo rather than
erythro.In
textile processing
Concentrated aqueous
solutions of Zinc chloride (more than 64%
weight/weight Zinc chloride
in water) have the interesting property
of dissolving starch, silk,
and cellulose. Thus, such solutions cannot be
filtered through standard filter papers. Relevant to its affinity
for these materials, Zinc chloride
is used as
a fireproofing agent and in fabric "refresheners"
such as Febreze.Zinc chloride
is used
for Friedel Craft Reaction,
Azotropic or Azeotropic Distillation, Desiccation & Karl Fischer.
Zinc -
Clinical Pharmacology
Zinc is
an essential nutritional
requirement and serves as a
cofactor for more than 70
different enzymes including
carbonic anhydrase, alkaline
phosphates, lactic
dehydrogenase, and both RNA
and DNA polymerase. Zinc
facilitates wound healing,
helps maintain normal growth
rates, normal skin
hydration, and the senses of
taste and smell.
Zinc
resides in muscle, bone,
skin, kidney, liver,
pancreas, retina, prostate
and particularly in the red
and white blood cells. Zinc
binds to plasma albumin,α2-macroglobulin,
and some plasma amino acids
including histidine,
cysteine, threonine, lysine,
and asparagine. Ingested
Zinc is excreted mainly in
the stool (approximately
90%), and to a lesser extent
in the urine and in
perspiration.
Providing
Zinc helps prevent
development of deficiency
symptoms such as:
Parakeratosis, hypogeusia,
anorexia, dysosmia,
geophagia, hypogonadism,
growth retardation and
hepatosplenomegaly.
The
initial manifestations of
hypoZincemia in TPN are
diarrhea, apathy and
depression. At plasma levels
below 20 mcg Zinc/100 mL
dermatitis followed by
alopecia has been reported
for TPN patients. Normal
Zinc plasma levels are 100 ±
12 mcg/100 mL.
Zinc 1
mg/mL (Zinc Chloride
Injection, USP) is a
sterile, nonpyrogenic
solution intended for use as
an additive to intravenous
solutions for total
parenteral nutrition (TPN).
Each mL of solution contains
2.09 mg Zinc chloride and 9
mg sodium chloride. The
solution contains no
bacteriostat, antimicrobial
agent or added buffer. The
pH is 2.0 (1.5 to 2.5);
product may contain
hydrochloric acid and sodium
hydroxide for pH adjustment.
The osmolarity is 0.354
m0smoL/mL (calc.).
Zinc
Chloride, USP is chemically
designated ZnCl2,
a white crystalline compound
freely soluble in water.
USES
Dry Cell or Batteries:
Zinc chloride is commonly used in dry cell batteries
as an electrolyte where it also acts as a moisture absorbent and
corrosion inhibitor.
It
is an excellent water
soluble Zinc source for uses compatible with chlorides. Chloride
compounds can conduct electricity when fused or dissolved in water.
Chloride materials can be decomposed by electrolysis to chlorine gas
and the metal. They are formed through various chlorination
processes whereby at least one chlorine anion (Cl-) is covalently
bonded to the relevant metal or cation. It is generally
immediately available in most volumes and high purity.
A Zinc chloride battery is a heavy duty variation of a zinc
carbon battery. It is used in applications that require moderate to
heavy current drains. These batteries have better voltage
discharge per time characteristics and better low temperature
performance than carbon zinc batteries. These batteries are
used in radios, flashlights, lanterns, fluorescent lanterns, motor
driven devices, portable audio equipments, communications
equipments, electronic games, calculators, and remote control
transmitters.
Electroplating : Today, there are three primary types of acid zinc plating
baths: straight ammonium chloride, straight potassium chloride and
mixed ammonium chloride/potassium chloride. Acid zinc plating
systems have several advantages over alkaline cyanide and alkaline
non-cyanide zinc plating systems except that in acid zinc plating,
the electrolyte is extremely corrosive.
Ammonium chloride zinc plating. The ammonium chloride bath
is the most forgiving of the three major types of acid zinc plating
because of its wide operating parameters. The primary drawback of
this system is the high level of ammonia, which can cause problems
in wastewater treatment. Ammonia acts as a chelator, and if the
rinse waters are not segregated from other waste streams, removal of
metals to acceptable levels using standard water treatment practices
can be difficult and expensive. Ammonia is also regulated in many
communities.
Potassium chloride zinc plating. Potassium chloride zinc
plating solutions are attractive because they contain no ammonia.
The disadvantages of this system are a greater tendency to burn on
extreme edges and higher operating costs. The potassium bath also
requires the use of relatively expensive boric acid to buffer the
solution and prevent burning in the high-current-density areas,
functions performed by the ammonium chloride in the other systems.
Mixed ammonium chloride/potassium chloride zinc plating.
This bath combines the best of the ammonia and ammonia-free baths.
Because potassium chloride is less expensive than ammonium chloride,
the maintenance costs of the mixed bath are lower than the ammonia
bath, and it does not require boric acid. The ammonia levels in the
rinse waters are low enough that it does not significantly interfere
with wastewater treatment, even if plating nickel and copper in the
same plant with mixed waste streams. If local regulations restrict
the level of ammonia discharged, special waste treatment equipment
will be required, and the non-ammonia bath is most likely the best
choice.
Galvanizing, Soldering and Tinning Fluxes:
Zinc chloride is used in fluxes for galvanizing, soldering and
tinning. Its ability to remove oxides and salts from metal surfaces
insures good metal to metal bonding. It has the ability to attack metal oxides (MO) to give
derivatives of the formula MZnOCl2.
This reaction is relevant to the utility of Zinc chloride
as a flux for soldering
- it dissolves oxide coatings exposing the clean metal surface.
Typically this flux was prepared by dissolving zinc foil in dilute
hydrochloric acid until the liquid ceased to
evolve hydrogen; for this reason, such flux was once known as killed spirits or "Marela".
Agriculture: It is very rarely used in
agriculture. It may be reacted with chelating agents to
form solutions of zinc that are biologically available to plants and
animals. It's the Chelate manufacturing that consumes Zinc chloride.
Petroleum: It is an excellent
emulsion breaker and is used to separate oil from water. It is also an effective packer
fluid in oil and gas wells due to its high specific gravity. However
its a little more costly than the other low specific gravity fluids
used in the process.
Water Treatment: It is used in
specialty corrosion inhibitors in cooling towers, potable water, and
in gas and oil wells.
Resins: It is used in Ion
- Exchange resins production.
Paints: It is used in for
the production of lithopone and as pigment for zinc chromate.
Rubber: It is used as
accelerator in the vulcanizing process of rubber.
Glue, wood working:
Zinc chloride is used in for
the preservation of glue, and for the impregnation of timber.
Printing: It is used in off-set
in the chemical products.
Odor Control: It reacts with sulfide to
minimize release of H2S gas in waste treatment facilities.
Oil-Gas Wells: High-density solutions of Zinc Chloride and calcium chloride give good performance
in well completion and work-over operations; the solutions also used
as packer fluids under certain well conditions. ZnCl2 has
been used in specialty corrosion inhibitors and invert emulsion
breakers.
Vulcanized Fiber & Reclaimed Rubber: Water-leaf paper is
gelatinized with zinc chloride solution is lesstacky, drier and less
moisture-absorbent than caustic reclaimed rubber. The ZnCl2 not only dissolves the cellulosic fibers in
the scrap, but also catalyzes depolymerization of the
elastomer.Similar method is used for Rubber reclaimed from natural,
styrene-butadiene rubber (SBR), and mixed scrap
Animal drug: It is used for
the production of zinc bacitracin.
Herbicide: Zinc chloride is used as an herbicide. It is
used to control lichen and moss growing on the roofs of houses and
other domestic dwellings, along walks, driveways, fences, and
wherever moss grows
Chemical: Zinc Chloride is used in the
production of ethylacetate. It is used as
condensing agent for the production of organic dye-stuff.
It is used as a stabilizing agent
for diazonium compounds. It is used for
the production of active carbon. Zinc
Chloride is used for Friedel Craft
Reaction, Azotropic or
Azeotropic Distillation, Desiccation &
Karl Fischer. Zinc laurate, linoleate Stearate or resinate can be
formed from zinc chloride solutions and solutions of the
corresponding sodium salt. It is a Lewis acid and
therefore electrophilic in character. Its catalytic activity is
milder than that of aluminum chloride in, for example,
Friedel-Crafts type reactions. It is particularly
effective in catalyzing reactions that eliminate molecules of water,
ammonia or mercaptans. Zinc chloride solutions gelatinize cellulosic
materials and induce crosslinking in such polymer formers as the
methylol ureas. It absorbs readily on charcoal or silica
for catalyzing acylations and alkylations by Friedel-Crafts
synthesis. In esterifications and condensation reactions, it facilitates the elimination
of water or ammonia molecules from the reactants. One example is the
Fischer idole synthesis.
Miscellaneous:
Zinc chloride has been used as a catalyst in
production of methylene chloride from methyl alcohol.
In the textile industry it
has found use in resin systems to impart durable press to cotton and
synthetic fabrics.
It has been used in reclaiming
rubber where it dissolves rayon cord.
In conjunction with sodium dichromate it has made an excellent wood
preservative.
Zinc chloride has found use in the manufacture of
glue, diazo dyes, paper, cosmetics, rayon, synthetic fibers,
disinfectants and fire fighting foam.
In ore refining it has been used as a flotation
agent.
It is an excellent source of zinc as a
starting material in the production of other zinc chemicals and is
an effective catalyst for removing molecules of water, ammonia or mercaptants.
Zinc chloride is used for
Friedel Craft Reaction,
Azotropic or Azeotropic Distillation, Desiccation & Karl Fischer.
In the laboratory, Zinc chloride finds wide use, principally as a
moderate-strength Lewis acid. It can catalyze the Fischer indole
synthesis and also Friedel-Crafts acylation reactions involving
activated aromatic rings.
Related to the latter is the classical preparation of the dye
fluorescein from phthalic anhydride and resorcinol, which involves a
Friedel-Crafts acylation.
Hydrochloric acid alone reacts poorly with primary alcohols and
secondary alcohols, but a combination of HCl with ZnCl2
(known together as the "Lucas reagent") at 130°C is effective for
the preparation of alkyl chlorides. This probably reacts via an SN2
mechanism with primary alcohols but via SN1 with
secondary alcohols.
Zinc chloride is also able to activate benzylic and allylic
halides towards substitution by weak nucleophiles such as alkenes
In similar fashion, Zinc Chloride ZnCl2 promotes selective NaBH3CN
reduction of tertiary, allylic or benzylic halides to the
corresponding hydrocarbons.
Zinc chloride is also a useful starting point for the synthesis of
many organozinc reagents, such as those used in the palladium catalyzed
Negishi coupling with aryl halides or vinyl halides. In such cases the
organozinc compound is usually prepared by transmetallation from an
organolithium or a Grignard reagent.
Zinc enolates, prepared from alkali metal enolates and ZnCl2,
provide control of stereochemistry in aldol condensation reactions due
to chelation on to the zinc. This is because the chelate is more stable
when the bulky phenyl group is pseudo-equatorial rather than
pseudo-axial, i.e., threo rather than erythro.
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