So for context, 会長 doesn't like the speaker and the speaker just said something to make 会長 think even less of him. Could someone give an explanation on why それに is directly following a verb and what its doing.
「会長{かいちょう}の目{め}つきが汚物{おぶつ}を見{み}るそれに変{か}わった。」
「会長{かいちょう}の目{め}つきが汚物{おぶつ}を見{み}るそれに変{か}わった。」
The core structure of this sentence is:
「X が Y に変わった。」
"X turned into Y."
X = 会長の目つき
Y = （人が）汚物を見る目つき
In order to avoid using 「目つき」 twice, the author is using 「それ」 here. The same thing actually happens in English as well using "that" or "those".
"The chairman's expression turned into that of a man looking at filth."
「汚物を見る」 functions as a relative clause that modifies 「それ」.
Other examples:
「ロシアの冬{ふゆ}は日本のそれよりも寒{さむ}い。」 ("The winters in Russia are colder than those in Japan.")
「あの人の音楽{おんがく}の趣味{しゅみ}は私のそれとは全{まった}く異{こと}なっている。」 ("That guy's taste in music is completely different from that of mine.")
「繁栄{はんえい}する会社{かいしゃ}と、衰退{すいたい}するそれとの違{ちが}いは何{なん}でしょうか。」 ("What are the differences between companies that flourish and those that decline?")
