-
PART 2 BIOCHEMICAL
PHARMACEUTICALS
生化制药
Unit 6 Isolation of Caffeine from Tea
从茶叶中分离咖啡因
In this
experiment, Caffeine will be isolated from tea
leaves.
在这个实验中，咖啡因会从茶叶中分离出来。
The major problem of the isolation is
that caffeine does not occur alone in tea leaves,
but is
accompanied by other
natural substances
from
which it must be separated.
分离过程中的主要问题就是，
茶叶中不仅仅只有咖啡因，
还伴
随着需要被分离除去的其
他天然物质。
The major
component
of tea leaves is
cellulose
，
which
is the major structural material of all
plant cells.
茶叶中
的主要成分是所有植物细胞中的主要结构材料
——
纤维素。
Cellulose is a
polymer
of glucose.
纤维素是葡萄糖的聚合物。
Since
cellulose
is
virtually
insoluble
in
water,
it
presents
no
problems
in
the
isolation
procedure.
然而纤维素实际上是不溶于水的，所以在隔离的程序上不用考
虑去除纤维素。
Caffeine, on the
other hand, is water soluble and is one of the
major substances
extract
ed
into the solution called
另一方面，咖啡因是水溶性的，也是萃取到溶液（也就是茶）里的主要物质之一。
Caffeine
comprise
s as much as 5 percent by
weight of the leaf material in tea plants.
咖啡因包含了茶树叶片材料总重的
5
%
之多。
Tannins
also
dissolve
in the hot water used to
extract tea leaves.
丹宁（鞣酸）也溶解于用于萃取茶叶的热水中。
The term tannin does not refer to a
single
homogeneous
compound,
or even to substances
which have
similar chemical structure.
丹宁一词不是指单个均一的化合物，也不是具有相似化学结构的物质。
It refers to a class of compounds which
have certain properties in common.
它是指某些具有共同属性的化合物的种类。
Tannins are
phenolic
compounds having
molecular weights
between
500 and 3000.
丹宁是一类分子质量在
500
到
3000
的
含酚的化合物。
They are widely used
to
它们被广泛用于鞣革。
They
precipitate
alkaloids
and proteins
from
aqueous solutions
.
它们从水溶液中沉淀出生物碱和蛋白质
Tannins are usually divided into two
classes: those which can be
hydrolyzed
and those which
cannot.
丹宁通常被分为两类：可水解和不可水解。
Tannins of the first type which are
found in tea generally yield glucose and
gallic acid
when
they are hydrolyzed.
在茶中，第一类丹宁水解后通常产生葡萄糖和五倍子酸。
These tannins are esters of gallic acid
and glucose.
这些丹宁是五倍子酸和葡萄糖的酯类。
They
represent
structures
in
which
some
of
the
hydroxyl
groups
in
glucose
have
been
esterified
by
digalloyl groups
.
它们代表着葡萄糖中的一些羟基被酯化为鞣酰基的结构。
The non-hydrolyzable tannins found in
tea are
condensation
polymers of
catechin
.
茶中的不可水解的丹宁是儿茶酚的缩合聚合物。
These
polymers
are
not
uniform
in
structure,
but
catechin
molecules
are
usually
linked
together at ring
positions 4 and 8.
这些聚合物在结构上是不一致的，但儿茶酚分
子通常在环的
4
号和
8
号位是相连的。
When tannins are
extracted into hot water, the hydrolyzable ones
are partially hydrolyzed,
meaning that
free gallic acid is also found in tea.
当丹宁被萃取到热水中，可水解的部分水解掉了，意味着茶中还有多余的五倍子酸。
The tannins,
by
virtue of
their phenolic groups, and
gallic acid by virtue of its
carboxyl
groups
,
are both acidic.
由于丹宁中含有酚，五倍子酸中含有羧基，所以它们都是酸性
的。
If
calcium
carbonate
,
a
base,
is
added
to
tea
water,
the
calcium
salts
of
these
acids
are
formed.
如果茶水中加入碳酸钙，这些酸的钙盐就会形成。
Caffeine can be extracted from the
basic tea solution with
chloroform
, but the calcium salts
of
gallic
acid
and
the
tannins
are
not
chloroform
soluble
and
remain
behind
in
the
aqueous
solution.
咖啡因可以被茶的氯仿溶液萃取，
但五倍子酸和丹宁的钙盐是不溶于氯仿的，
所以它们
< br>会留在水溶液中。
The brown color
of a tea solution is due to
flavonoid
pigments
and
chlorophylls
, as well as
their respective
oxidation
products
.
茶水呈现出褐
色是由于黄酮类色素和叶绿素，以及它们各自的氧化物。
Although
chlorophylls
are
somewhat
chloroform
soluble,
most
of
the
other
substances
in
tea are not.
虽然叶绿素是微溶于氯仿的，但茶叶中的其他大多数物质不是如此。
Thus, the chloroform extraction of
the basic tea solution removes nearly pure
caffeine.
因此，碱性茶水的氯仿提取去除了几乎无杂质的咖啡因。
The chloroform is easily removed
by
distillation
(by 61'C) to
leave the crude caffeine.
氯
仿在
61
℃蒸馏中易被去除，从而分离出咖啡因的粗产物。
The caffeine may be purified
by
recrystallization
or by
sublimation
.
咖啡因可以通过结晶或升华来纯化。
In a second part of this experiment,
Caffeine will be
convert
ed
to a
derivative
.
本次实验的第二个部分，咖啡因会被转化为衍生物。
A derivative of a compound is a second
compound, of known
melting
point
, formed from
the
original compound by a simple chemical reaction.
一个化合物的衍生物是一个已知熔点的第二化合物，
是由原来的化合物通过简单化学反
应生成的。
In trying to
make a positive identification of an organic
compound, it is often customary to
convert it into a derivative.
为了试图鉴定原始化合物，我们通常习惯将它转化成衍生物。
If the first compound, Caffeine in this
case, and its derivative both have melting points
which
match those reported in the
chemical
literature (e. g.,
a handbook), it is assumed that there is no
coincidence and that the identity of
the first compound, Caffeine, has been definitely
established.
如果第一化合物
（在这也就是指咖
啡因）
以及它的衍生物的熔点都与化学文献上所记载
的相匹配，
那么就可以推测第一化合物就是咖啡因无疑。
Caffeine is a base and will react with
an acid to give a salt.
咖啡因是碱，可以和酸反应生成盐。
Using
salicylic
acid
, a derivative salt of Caffeine,
Caffeine salicylate, will be made in order to
establish the identity of the Caffeine
isolated from tea leaves.
和水杨
酸反应就能生成咖啡因的一种衍生物盐，叫做水杨酸咖啡因。它可以用来鉴定
茶叶中分离
出的咖啡因。
Special Instructions
特别注意
Be careful
when handling chloroform.
要小心处理氯仿。
It is a
toxic solvent
, and you
should not breathe it
excessively
or spill it on
yourself.
它是一种有毒溶剂，应防止过度吸入以及洒在身上。
When discarding spent tea leaves, do
not put them in the sink because they will clog
the
drain.
丢弃茶叶时，不应将它们扔在水槽，因为它们会堵塞排水管。
Dispose of them in a waste container.
应该将它们扔入垃圾桶。
Procedure
程序
Place 25g of dry tea leaves, 25g of
calcium carbonate powder, and 250ml of water in a
500ml
three neck round bottom
flask
equipped with a
condenser
for
reflux
.
< br>将
25
克干燥茶叶、
25
克碳酸钙粉末和
250
毫升水混入一个装有回
流冷凝管的
500
毫升
三口圆底烧瓶。
Stopper
the
unused openings in the flask and heat the mixture
under reflux for about 20
minutes.
将烧瓶中未使用的开口塞住，加热混合物，回流
20
分钟。
Use
a
Bunsen burner
to heat.
用本生灯加热。
While the solution is still hot, filter
it by gravity through a
fluted
filter
using a fast filter paper
such as E&D No. 617 or S&S No. 595.
用快速过滤纸如
E&D No.
617
或
S&S No.
595
，通过凹槽过滤器，趁热过滤。
You may need to change the filter paper
if it clogs.
如果堵住了就需要换一种滤纸。
Cool the
filtrate
(filtered liquid) to room temperature and, using a
separatory funnel
, extract
it twice with 25ml portions of
chloroform.
待滤液降至室温，用
25
毫升氯仿在分液漏斗中萃取两次。
Combine the two portions of chloroform
in a 100ml round bottom flask.
将两次萃取的了氯
仿倒入
100
毫升圆底烧瓶中混合。
-
-
-
-
-
-
-
-
-
上一篇：英语面试121问
下一篇：考研复试：英语口语常问的16个问题-附回答模板!讲课稿