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Патент USA US2406960

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Patented Sept. 3, 1946
2,406,960
UNITED STATES PATENT OFFICE
2,406,960
'
‘
PREPARATION OF HEAVY METAL SALTS
OF DITHIOCARBANHC ACIDS
Arthur M. Neal, Wilmington, Del" and Bernard
M. Sturgis, Pitman, N. J.,. assignors to E. I. ‘
du Pont de Nemours & Company, Wilmington,
Del., a corporation of Delaware
No Drawing. ‘Application August 22, 1942,
,
Serial No. 455,784
17 Claims. (01. 260-239)
1
,
This invention relates to the preparation of“
heavy metal salts of dithiocarbamic acids and
more particularly to aprocess for preparing heavy
metal salts of dithiocarbamic acids of ‘improved
appearance and quality.
5
Heavy metal salts, particularly zinc salts, of di
,
2
or lumps or other impurities. Products, possess
ing these various defects, are inferior in quality
and require extra costly steps, such as grinding
and screening, in order to render them satisfac
tory forusep
,
,
It is ‘an object of the present invention to pro
thiocarbamic acids have long been used as ac
vide an improved process for preparing heavy
celerators for the vulcanization of rubber. These
metal salts of dithiocarbamic acids. Another ob
compounds are very effective in the vulcaniza
ject is to provide a process for the preparation of
tion of both dry rubber and rubber latex. For 10 heavy metal salts of dithiocarbamic acids with
improved appearance and of better quality par
use in dry rubber, these dithiocarbamates must
be in the form of very ?nely divided powders, free
ticularly adapted ‘for use as accelerators for the
from lumps or agglomerates, in order that they
vulcanization of rubber. A further object is to
may be dispersed thoroughly and uniformly
provide a process for preparing heavy metal salts
throughout the rubber. The presence of lumps l5 of dithiocarbamic acids of higher purity and
of accelerator in the rubber results in spotty and
more? uniformly ?nely divided character which
will more readily disperse in rubber. A still fur- uneven cures, giving inferior vulcanizates. _For
ther object is to provide a method for preparing
use in rubber latex also, a ?nely divided powder
is desired. In the preparation of. zinc salts of
heavy metal salts of dithiocarbamic acids from
dithiocarbamic acids, a white color is desired for 20 more highly concentrated solutions of soluble di
the product. The presence of brown specks or
thiocarbamates. Other objects are to advance
lumps throughout the product is obviously dis
the art. Stillother objects will appear herein
advantageous in the compounding of white or
after.
7
,
The above and other objects of our invention
light colored rubber stocks. Furthermore. the
presence of impurities in the product is very det- 25 maybe accomplished by precipitating a heavy
metal salt of a dithiocarbamic acid from a solu
rimental since these impurities tend to activate
or retard the accelerator and thus affect the rate
of cure of the compounded rubber.
‘
" ‘v
tion of a soluble salt of the dithiocarbamic acid
‘ in the presence of a salt of a strong base and a
weak acid. We have found that, by incorporat
Heavy metal salts of dithiocarbamic acids,
particularly zinc salts, form a well known class 30 ing a small proportion of a water-soluble salt of
a strong base and a weak acid in the aqueous so
of chemical compounds. The usualmethod of
lution of a water-soluble salt of the dithiocar
preparing such compounds consist ?rst in the
preparation ofan aqueous solution of a soluble
bamic acid before adding a water-soluble salt
ofthe heavy metal for the purpose of precipitat
dithiocarbamate by reacting an amine with car
bon disul?de and a base such as an alkali metal 35 ing the ‘heavy metal salt of the dithiocarbamic
acid, a great improvement in the appearance,
hydroxide. This solution of soluble dithiocar
purity,pparticle size and general quality of the.
bamate is then treated with a soluble salt of
heavy metal salts of the dithiocarbamic acids can
a heavy metal, such as zinc sulfate, whereuponthe
be obtained. Under such circumstances, the
heavy meta1 salt of the dithiocarbamic acid pre
This proc- 40 heavy metal salts of the dithiocarbamic acids are
usually precipitated in a much ?ner form, free of
lumps and agglomerates, free from waxy and
to a satisfactory product.
_ ‘
H‘ ‘
‘
sticky materials .and free from brown specks and
In the preparation of these heavy metal vsalts
cipitates and is filtered, off and dried.
ess is relatively simple, but does not always lead
like impurities. We have also found that, by
of dithiocarbamic acids by the usual methods, the
resulting product is often lumpy and full of hard 45 employing the small amount of the salt of a
strong base and a Weak acid, we can employ high
granules and agglomerates which are exceedingly
er concentrations of reactants than have been
dif?cult to break up. Often, the product will be
permissible heretofore since the precipitate is
waxy in nature or form waxy lumps that are dif
?cult to ?lter and dry. Sometimes the heavy
obtained in a liner form whereby it can be read
metal salts tend to precipitate in a‘ gummy form, 50 ily agitated. Heretofore, it has been necessary
to precipitate the heavy metal salts from quite
sticking to the agitator and the sides of. there
action vessel and forming soft balls.
Some of
them, especially if the amine used in preparing
the dithiocarbamic acid was not entirely pure,
dilute‘ solutions ‘of thetdithiocarbamates as other
wise the precipitate would become so thick that
it could not be agitated with any degree of suc
give heavy metal salts containing brown specks 55 Cess. Furthermore, by carrying out the process
3
2,406,960
4
in accordance with our invention, it is possible
to prepare satisfactory heavy metal salts of di
thiocarbamic acids where the soluble dithiocar
bamates have been prepared from amines of
somewhat lower purity than was heretofore pos
siblc.
Our improved process may be employed to ad~
vantage in the preparation of the heavy metal
sociation constant at least as great as 1><10-2.
By a weak acid, we mean an inorganic acid or a
monocarboxylic organic acid having a dissocia
tion constant between 1><10—6 and 1><10~3 and
dibasic organic acids having dissociation con
stants between 1><l0—6 and 5><10-2. Suitable
vbases are sodium hydroxide, potassium hydrox
ide, lithium hydroxide, tetra-methyl ammonium
salts from any of the common water-soluble salts
hydroxide and the like.
of dithiocarbamic acids, but is particularly adapt
particularly acetic acid, propionic acid, butyric
acid, isobutyric acid, caproic acid, valeric acid,
capric acid, salicylic acid, oxalic acid, formic
ed to the preparation of the heavy metal salts of
N-aliphatic dithiocarbamic acids. The- dithio
carbamic acids are represented by the‘ formula
R
Suitable acids include
acid, fumaric acid, lactic acid and the like. We
particularly prefer the salts of the strong bases
with the weak lower saturated aliphatic acids.
i
\N——C—S-—H
By lower aliphaticacids, We mean those contain
ing from 1 to 6 carbon atoms. The preferred
salt of a strong base and a weak acid is sodi
R
wherein at least one R represents an organic
group and the other R represents hydrogen or
an organic group and wherein both R’s together
may represent a cyclic group. Each R may rep
resent an aliphatic radical or the two R’s may
um acetate.
The salts of the strong bases and weak acids
will generally be employed in the proportion of
from about 1% to about 20% based on the weight
of the soluble dithiocarbamate. Preferably, we
employ the salt in the proportion of from about
6% to about 15% of the weight of the soluble di
represent a hydrocarbon chain having the ter
minal carbon atoms thereof attached to the ni
trogen to form a hetero-cyclic ring, as in hexa
methylene dithiocarbamic acid and pentamethyl
ene dithiocarbamic acid, wherein hexamethylene
and pentamethylene mean the divalent radicals
thiocarbamate. Generally, the addition of from
--CH2(CH2)4CH2— and —CH.2(C‘H2)3CH2—~, re
of salt. By a Water-soluble salt of a strong base
and a- weak acid, we mean one which is soluble in
about 1 to about 3 parts of the salt to each 100
parts of solution will provide the desired amount
spectively.
The water-soluble salts of the dithioarbamic
water to the extent‘ of at least 1%. Also, it is
acids include sodium, potassium, calcium, barium,
usually desired that the salt be derived from a
weak acid which is soluble in Water to the ex
tent of at least 2% so as to avoid contamination
ammonium and amine salts. As is usual in such
a process, it will generally be preferred to employ . .
of the precipitate with acid which may be liber
ated during the reaction.
the sodium. salts of the dithiocarbamic acids.
Also, as is usual, the soluble salts of-the dithio
carbamic acids will be dissolved in an aqueous
solvent, preferably water, in the desired concen
tration. These solutions may contain 10% or
less of the soluble salts of the dithiocarbamic
acids. However, in our process it is possible to
employ more highly concentrated solutions of the
soluble dithiocarbamates and we preferablyem
In order to more clearly illustrate our inven
tion, the preferred modes of carrying the same
into effect and the advantageous results to be
obtained thereby, the following examples are
given:
Example I
200 parts of a 10% solution of sodium hexa
ploy solutions containing from about 10% to. , methylene dithiocarbamate, having a pH of 9.0,
about 30% of the soluble dithiocarbamates. Also, '
was stirred at 30° C. while a 20% solution of zinc
the, solutions should have a pH above 7 and pref
sulfate was‘slowly dropped in until precipitation
erably a pH of from 7 to about 11.5.
was complete. A rather gel-like precipitate was
Any of the water-soluble heavy metal salts,
formed which later became lumpy. The precipi
ordinarily employed as the precipitating agents in
tate, stuck to the stirrer and the reaction vessel,
‘the manufacture of heavy metalsalts of dithio
and, after ?ltration and drying, was lumpy and
carbamic acids, may be employed. It.is only
full of small hard particles.
necessary that the heavy metal salt, in solution,
Example‘ II
will form heavy metal ions which will be avail
able for precipitation and that the heavy metal
To 200 parts of the sodium hexametliylene di
will form stable salts with the dithiocarbamic 55 thiocarbamate solution of Example I was added
acids. Suitable heavy metals are zinc, cadmium,
2 parts of sodium acetate. The resulting solu
mercury, lead, iron and the like. We have found
tion had a pH of 8.8. A 20% solution of zinc
our invention to be particularly adapted to the
sulfate was then added with stirring at 30° C.
manufacture of zinc salts of the dithiocarbamic
until precipitation was complete. The resulting
acids. The heavy metal‘ salts may be any non 60 precipitate did not stick to the stirrer or the
oxidizing metal saltswhich are of sufficient solu
reaction vessel, and came down in a more ?nely
bility for the purpose. Such heavy metal salts
divided form. After drying, the zinc heXameth
are well known to the art. Our invention is par
ylene dithiocarbamate contained no lumps or hard
ticularly applicable where the precipitating agent
particles and was much softer and ?ner than that
is a heavy metal salt of a strong acid such as sul
of Example I.
furic acid and hydrochloric acid. However, it is
also applicable where the precipitant is a heavy
\
metal salt of a weak acid such as, for example,
200‘parts of a 10% sodium hexamethylene di
thiocarbamate solution, having a pH of ‘7.5, was
treated with 20% zinc sulfate as in Example I.
The product was full of hard‘ brown lumps.
Example IV
lead acetate.
Our improvement comprises incorporating into
the solution of the water-soluble dithiocarbam
ate, prior to precipitation by the addition of the
water-soluble heavy metal salt, a small propor
tion of a salt'of a strong base and a weak acid.
By a strong base, We mean a base having a dis- '
Example III
To 200 parts of the sodium hexamethylene di
thiocarbamate solution of Example III was added
2,406,960
5
' 6
2 parts of sodium acetate. The‘. resulting solu
tion had a pH of 8.8. The zinc hexamethylene di
‘ thiocarbamate solution, having apH of 11.0, was
stirred at room temperature while a. 10% solu
tion of zinc chloride was added. The resulting
thioearbamate was then precipitated as before.
It was a soft white powder containing no brown
Example V '
precipitate contained considerable gummy and
waxy material and was entirely unsatisfactory.
Example XIV
200 parts of a 10% solution of sodium dibutyl
dithiocarbamate was made just neutral to phe
The process of Example XIII was repeated ex
cept that 1 part of sodium acetate was added to
specks or lumps.
‘
5
nolphthalein, a pH of 10.0, and a 20% solution 10 the soluble dithiocarbamate, producing a pH of
of zinc sulfate added with stirring. The resulting
9.1, before precipitation. The resulting zinc hexa
zinc dibutyl dithiocarbamate was full of hard
methylene dithiocarbamate was in the form of
lumps after drying.
a ?ne white powder of satisfactory appearance
and quality.
,
Example VI
Example XV
The process of Example V was repeated except 15
that 3 parts of sodium formate was added to the
100 parts of a 15% solution of sodium diamyl
sodium dibutyl dithiocarbamate solution, produc
dithiocarbamate, having a pH of 9.5, was precipi
ing a pH of 9.9, before precipitation. The result
tated with a 15% solution of cadmium chloride.
ing zinc dibutyl dithiocarbamate was a ?ne white
The resulting‘ cadmium ‘diamyl dithiocarbamate
20 was lumpy and unsatisfactory.
powder containing no lumps or hard particles. .
'
Example XVI
, Example VII
The process of Example V was repeated except
The processiof Example XV was repeated ex
that 2.5 parts of sodium oxalate was added, pro
cept that 1 part of sodium acetate was added to
ducing a pH of 10.0. The resulting zinc dibutyl 25 the sodium diamyl dithiocarbamate solution be
dithiocarbamate was a ?ne white powder.
fore precipitation, producing a pH of 8.9. The
cadmium diamyl dithiocarbamate produced was >
Example VIII
in the form of a ?nely‘divided yellow powder.
The process of Example V was repeated except
that 2 parts of disodium salicylate was added be 30 . It will be understood that the foregoing exam
ples are given for illustrative purposes only and
fore precipitation, producing a pH of 11.4.- The
that our invention is not to be limited to the‘
resulting product was a; white powder free from
lumps.
'
speci?c embodiments disclosed therein.
->
Many
variations and modi?cations can be made, par
i
‘ Example IX
r ticularly in the ingredients and conditions em
150 parts of a 30% aqueoussolution of sodium
ployed, without departing from the spirit or scope
hexamethylene dithiocarbamate, having a pH of
of our invention. For example, other heavy metal
9.0, was stirred at 27° C. while a 20% solution of
salts of other dithiocarbarnic acids may be pre
zinc sulfate was slowly ‘dropped in. A rather ' pared in accordance with our invention. Some
curdy precipitate was formed, and, before the re
of such other heavy metal dithiocarbamates are:
40
action was complete, the contents of the beaker
Cadmium di-n~p-ropyl dithiocarbamate
Cadmium cyclohexyl dithiocarbamate
sulfate had to be stopped.
Mercuric hexamethylene dithiocarbamate
Example X
Zinc diamyl dithiocarbamate
The process of Example IX was’repeated ex 45 Cadmium dibenzyl dithiocarbarnate
Zinc dibenzyl dithiocarbamate
cept that 3 parts of sodium acetate were added
Zinc diallyl dithiocarbamate
to the sodium‘hexamethylene dithiocarbamate so
Lead Z-methyl pentamethylene dithiocarbamate
lution, producing a pH‘of 8.8, before precipitation.
became too thick to stir and theaddition of zinc
Ferric dibutyl dithiocarbamate
Lead pentamethylene dithiocarbamate
The precipitate came down in a much ?ner form
and no di?iculty was experienced ‘with the agi
tation at any time during the reaction.
.
- Ferric pentamethylene dithiocarbamate
'
It will be apparent that, by our invention, we
Example XI
have provided an’improved?method for the prep
200 parts of a 10% solution of sodium dieth
anol dithiocarbamate was made just basic to phe
aration of heavy metal salts of dithiocarbamic
nolphthalein, a pH of 10.5, andthen precipitated 55 acids from the water-soluble salts of such acids,
whereby products of greatly improved appear
with 20% zinc sulfate solution while being rapidly
ance and quality are obtained. Furthermore, by
our invention, we have made it possible'to em
stirred. The product was very gummy and sticky.
It ?ltered with great difficulty, and remained
gummy after drying.
>
‘
~
>
>
ploy more highly concentrated solutions of the
»
Example XII
60
soluble dithiocarbamates andpalso to employ solu
~tions of lower puritypwhile still obtaining highly
The process of Example XI was repeated ex
cept that 3 parts of sodium acetate was added
satisfactory products; We, therefore, believe that
.before precipitation, producing a pH of 9.0. The
vancevin the art.
resulting zinc. diethanoldithiocarbamate was in (i5
our invention constitutes a very material vad
We
claim:
,
7
V
,
‘
1. The process of preparing a heavy metal salt
of a dithiocarbamic acid which comprises adding
from about 1% to about 20% of a ‘water-soluble
Example ,XIII
salt of a strong base and a weakracidp to an
‘ ' 50 parts of a crude aqueous solution of hexa 70 aqueous solution of a water-soluble salt of the
methylene 'imine,.containing 37% hexamethylene
dithiocarbamic acid having a pH above. 7 and
imine, 2.5% ammonia, and small amounts of a
then adding a water-soluble salt of the heavy
number of impurities was converted into sodium
metal to the solution in su?icient amount to pre
the form of. a ?ne white powder which ?ltered
well and dried to give a satisfactory product.
hexamethylene dithiocarbamate by reaction with
carbon disul?de and sodium hydroxide. This-die
cipitate the heavy, metal salt. of the ‘ dithiocar~
bamic acid.
2,406,960
8
of a water-soluble salt of the dithiocarbamic acid
having a pH of from about '7 to about 11.5 and
then adding a water-soluble salt of the heavy
metal and a strong acid to the solution in suf
2. The’process of preparingaheavy metal salt
of a dithiocarbamic acid which comprises add
ing from about 1% to about 20% of a water
soluble salt of a strong base and a weak acid to
an aqueous solution of a water-soluble salt of
the dithiocarbamic acid having a pH of from '7
Cl
?cient amount to precipitate the heavy metal salt
of the dithiocarbamic acid.
10. The process of preparing a heavy meta1 salt
of a dithiocarbamic acid which comprises add
ing from about 1% to about 20% of a water
?cient amount to precipitate the heavy metal
10 soluble salt of a strong base and a weak lower
salt of the dithiocarbamic acid.
saturated aliphatic carboxylic acid to an aqueous
3. The process of preparing a heavy metal salt
solution of a water-soluble salt of an N-aliphatic
of a dithiocarbamic acid which comprises adding
dithiocarbamic acid having a pH of from 7 to
from about 1% to about 20% of a water-soluble
about 11.5 and then adding a Water-soluble salt
salt of a strong base and a weak acid .to an
of the heavy metal and a strong acid to the so
aqueous solution of a water-soluble salt of an
lution in su?icient amount to precipitate the heavy
N-aliphatic dithiocarbamic acid having a pH of
from 7 to about 11.5 and then adding a water
metal salt of the dithiocarbamic acid.
11. The process of preparing a heavy metal
soluble salt of the heavy metal and a strong acid
salt of hexamethylene dithiocarbamic acid which
to the solution in suflicient amount to precipitate
comprises adding from about 1% to about 20%
the heavy metal salt of the dithiocarbamic acid.
4. The process of preparing a heavy metal salt
of a water-soluble salt of a strong base and a
of a dithiocarbamic acid which comprises adding
weak lower saturated aliphatic carboxylic acid
from about 1% to about 20% of a water-soluble
to an aqueous solution of a water-soluble salt of
hexamethylene dithiocarbamic acid having a pH
salt of a strong base and a weak acid to an
aqueous solution of a water-soluble salt of hexa
of from 7 to about 11.5 and then adding a Water
methylene dithiocarbamic acid having a pH of
soluble salt of the heavy metal and a strong acid
from '7 to about 11.5 and then adding a water
to the solution in su?icient amount to precipitate
soluble salt of the heavy metal and a strong acid
the heavy metal salt of the dithiocarbamic acid.
to the solution in su?icient amount to precipitate
12. The process of preparing the zinc salt of
to about 11.5 and then adding a water-soluble
salt of the heavy metal to the solution in suf
the heavy metal salt of the dithiocarbamic acid.
5. The process of preparing the zinc salt of a
a dithiocarbamic acid which comprises adding
from about 1% to about 20% of a water-soluble
dithiocarbamic acid which comprises adding
salt of a strong base and a weak lower saturated
from about 1% to about 20% of a water-soluble
aliphatic carboxylic acid to an aqueous solution
salt of a strong base and a weak acid to an aque
of a water-soluble salt of the dithiocarbamic acid
ous solution of a water-soluble salt of the dithio
having a pH of from '7 to about 11.5 and then
carbamic acid having a pH of from 7 to about
adding a water-soluble zinc salt of a strong acid
11.5 and then adding a water-soluble zinc salt of
to the solution in su?icient amount to precipitate
a strong acid to the solution in sui?cient amount
the zinc salt of the dithiocarbamic acid.
to precipitate the zinc salt of the dithiocarbamic
13. The process of preparing the zinc salt of
40 a dithiocarbamic acid which comprises adding
acid.
6. The process of preparing the zinc salt of
from about 1% to about 20% of a water-soluble
a dithiocarbamic acid which comprises adding
salt of a strong base and a Weak lower saturated
from about 1% to about 20% of a water-soluble
aliphatic carboxylic acid to an aqueous solution
salt of a strong base and a weak acid to an aque
of a water-soluble salt of an N-aliphatic dithio
ous solution of a water-soluble salt of an N-ali
carbamic acid having a pH of from '7 to about
phatic dithiocarbamic acid having a pH of from '7
11.5 and then adding water-soluble zinc salt of a
to about 11.5 and then adding water-soluble zinc
strong acid to the solution in su?icient amount to
salt of a strong acid to the solution in sufficient
precipitate the zinc salt of the dithiocarbamic
amount to precipitate the zinc salt of the dithio
acid.
carbamic acid.
50
14. The process of preparing the zinc salt of
hexamethylene dithiocarbamic acid which com
'7. The process of preparing the zinc salt of
hexamethylene dithiocarbamic acid which com
prises adding from about 1% to about 20% of a
prises adding from about 1% to about 20% of a
water-soluble salt of a strong base and a weak
lower saturated aliphatic carboxylic acid to an
water-soluble salt of a strong base and a weak
acid to an aqueous solution of a water-soluble 55 aqueous solution of a water-soluble salt of hexa
methylene dithiocarbamic acid having a pH of
salt of hexamethylene dithiocarbamic acid hav
from 7 to about 11.5 and then adding a water
ing a DH of from 7 to about 11.5 and then add
soluble zinc salt of a strong acid to the solution
ing a water-soluble zinc salt of a strong acid to
the solution in sufficient amount to precipitate the
in suiiicient amount to precipitate the Zinc salt
zinc salt of the dithiocarbamic acid.
60 of the dithiocarbamic acid.
15. The process of preparing a heavy metal salt
8. The process of preparing a heavy metal salt
of a dithiocarbamic acid which comprises adding
of. a dithiocarbamic acid which comprises adding
from about 1% to about 20% of sodium acetate
from about 1% to about 20% of a water-soluble
to an aqueous solution of a water-soluble salt of
salt of a strong base and a weak lower saturated
aliphatic carboxylic acid to an aqueous solution 65 the dithiocarbamic acid having a pH above 7
and then adding a water-soluble salt of the heavy
of a water-soluble salt of the dithiocarbamic acid
metal and a strong acid to the solution in suf
having a pH above 7 and then adding a water
?cient amount to precipitate the heavy metal salt
soluble salt of the heavy metal and a strong acid
to the solution in suf?cient amount to precipitate
of the dithiocarbamic acid.
16. The process of preparing heavy metal salt
the heavy metal salt of the dithiocarbamic acid.
9. The process of preparing a heavy metal salt
of a dithiocarbamic acid which comprises add
of a dithiocarbamic acid which comprises adding
ing from about 1% to about 20% of sodium ace
from about 1% to about 20% of a water-soluble
tate to an aqueous solution of a water-soluble
salt of a strong base and a weak lower saturated
salt of the dithiocarbamic acid having a pH of
aliphatic carboxylic acid to an aqueous solution 75 ..from 7 to about 11.5 and then adding a water
9
2,406,960
soluble salt of the heavy metal and a strong acid
to the solution in sufficient amount to precipitate
the heavy metal salt of the dithiocarbamie acid.
17. The process of preparing ‘the zinc salt of
hexamethylene dithiocarbamic acid which com 5
prises adding from about 1% to about 20% of
sodium acetate to an aqueous solution of a water
10
‘
soluble salt of hexamethylene dithiocarbamic acid
‘having a pH of from '7 to about 11.5 and then add
ing a water-soluble zinc salt of a strong acid to
the solution in su?icient amount to precipitate
the zinc salt of the dithiocarbamic acid.
ARTHUR M. NEAL.
BERNARD M. STURGIS.
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